Overview: HMOs are managed care organizations that integrate the financing and delivery of healthcare, using specific structural mechanisms to control costs and coordinate care.

An HMO is a type of managed care plan that provides comprehensive health services to enrolled members, typically for a fixed prepaid premium. Two defining characteristics set HMOs apart from traditional indemnity insurance: (1) members must use providers within the HMO's network to receive coverage (with limited emergency exceptions), and (2) a primary care physician (PCP) acts as the member's "gatekeeper," coordinating all care and providing referrals to specialists.

How HMOs Control Costs

Gatekeeping is the cornerstone of HMO cost control. Because a patient must see their PCP before accessing specialty care, the PCP can often treat minor conditions in-office at a fraction of what a specialist charges. Gatekeeping also prevents redundant diagnostic testing that occurs when patients self-refer to multiple specialists simultaneously, and it keeps care coordinated through a single provider who knows the patient's full medical history.

Capitation fundamentally restructures how providers are paid. Rather than receiving a fee for each service rendered (fee-for-service), an HMO pays a provider a fixed dollar amount per enrolled member per month (PMPM) — regardless of how often that member seeks care. If the member never visits the doctor, the provider still receives the monthly payment. If the member requires extensive care, the provider absorbs the cost. This shifts financial risk from the insurer to the provider and aligns incentives toward keeping patients healthy and avoiding unnecessary procedures.

Utilization review (UR) acts as a system of checks on care delivery:

Prospective review (prior authorization) occurs before a planned procedure or expensive service — the HMO reviews the treatment request against clinical guidelines before agreeing to cover it
Concurrent review monitors ongoing care, especially during inpatient hospital stays, to ensure the patient is progressing appropriately and to coordinate discharge planning
Retrospective review analyzes claims after the fact to identify patterns of overutilization, billing errors, or care that deviated from evidence-based guidelines

The Four HMO Model Types

The same managed care philosophy can be implemented through four very different organizational structures, distinguished primarily by how the HMO relates to its physicians:

Staff model HMO: The HMO directly employs physicians as salaried workers and owns the facilities where care is delivered. Physicians work exclusively for the HMO and see only HMO members. Care is centralized — laboratory, radiology, pharmacy, and primary care may all exist under one roof. This model gives the HMO maximum control over care quality and cost but requires enormous capital investment to build and staff facilities. Pure staff-model HMOs are rare today. From the physician's perspective, the trade-off is a predictable salary and no administrative burden, but limited autonomy and capped income.

Group model HMO: The HMO contracts with a single large, multispecialty physician group — an independent organization that employs its own physicians. The HMO pays the group on a capitated basis (a fixed PMPM), and the group distributes payments to its doctors. Physicians are employees of the group, not the HMO. Care is delivered in the group's own facilities. This model reduces the HMO's capital requirements while maintaining strong integration, but it creates dependency on a single contracting partner. Kaiser Permanente is often cited as the most prominent example of this model type.

Network model HMO: The HMO contracts with multiple independent physician groups — not just one. Each group may see patients from other insurers as well as HMO members. This structure gives the HMO broader geographic coverage and reduces dependency on any single medical group, while offering members a wider choice of practice locations. However, managing quality and utilization across multiple independent groups is more challenging than in the staff or group models.

IPA model (Independent Practice Association): The HMO contracts not with individual physicians or physician groups directly, but with an Independent Practice Association (IPA) — a legal entity formed by independent, private-practice physicians who band together to contract with payers. Individual physicians remain in their own offices, see patients from multiple insurance plans, and retain their independence. The IPA is by far the most common HMO structure today. Cost control is maintained through capitation (the HMO pays the IPA a PMPM, which the IPA then distributes to its members), withhold mechanisms (a percentage of each physician's payment is held back and released only if the IPA meets overall cost and utilization targets), PCP gatekeeping, and utilization review. The IPA model is the most flexible and lowest-capital structure for an HMO but gives the insurer the least direct control over physician behavior.

Feature	Staff	Group	Network	IPA
Physician employment	HMO directly	Independent group	Independent groups	Independent (own offices)
HMO capital required	Highest	Moderate	Low	Lowest
HMO control over providers	Highest	High	Moderate	Lowest
Provider geographic flexibility	Lowest	Moderate	High	Highest
Provider autonomy	Lowest	Moderate	High	Highest
Common today?	Rare	Moderate	Yes	Most common

FAQ

If an HMO member goes to an emergency room out of network, is it covered?
Yes — true emergencies are covered regardless of network. Federal law (ACA) and most state laws require that emergency services be covered at in-network cost-sharing rates even at out-of-network facilities. The exception is non-emergency care: for that, an HMO member who self-refers to an out-of-network provider pays 100% of the cost with no insurance coverage.

What is the difference between the IPA model and the network model?
The IPA model contracts with an IPA — an intermediary association of independent solo or small-group physicians. The network model contracts directly with multiple independent physician groups (typically larger, multispecialty practices). In the IPA model, individual physicians keep their private offices and mixed patient panels; in the network model, the contracting unit is a group practice rather than individual physicians through an association.