Table 137Health maintenance organizations (HMOs) and enrollment, according to model type, geographic region, and Federal program: United States, selected years 1976–2004
[Data are based on a census of health maintenance organizations]
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Plans and enrollment 1976 1980 1985 1990 1995 1998 2000 2003 2004
All plans174235478572562651568435412
Model type:1
 Individual practice association24197244360332317278188176
 Mixed- - -- - -- - -- - -122212188145140
Geographic region:
Enrollment1Number of persons in millions
Model type:1
 Individual practice association20.41.76.413.720.132.633.427.924.6
 Mixed- - -- - -- - -- - -17.630.132.327.828.9
Federal program:4
 Medicaid5- - -
 Medicare- - -
Percent of HMO enrollees
Model type:1
 Individual practice association26.618.730.441.639.442.641.338.935.8
 Mixed- - -- - -- - -- - -34.539.239.938.742.0
Federal program:4
 Medicaid5- - -
 Medicare- - -
Percent of population enrolled in HMOs
Geographic region:

- - - Data not available.


Enrollment or number of plans may not equal total because some plans did not report these characteristics.


An HMO operating under an individual practice association model contracts with an association of physicians from various settings (a mixture of solo and group practices) to provide health services.


Group includes staff, group, and network model types. See Appendix II, Health maintenance organization.


Federal program enrollment in HMOs refers to enrollment by Medicaid or Medicare beneficiaries, where the Medicaid or Medicare program contracts directly with the HMO to pay the appropriate annual premium.


Data for 1990 and later include enrollment in managed care health insuring organizations.

NOTES: Data as of June 30 in 1976–80, and January 1 from 1990 onward. Open-ended enrollment in HMO plans, amounting to 6.9 million on January 1, 2004, is included from 1994 onward. See Appendix II, Health maintenance organization. HMOs in Guam are included starting in 1994; HMOs in Puerto Rico, starting in 1998. In 2004 HMO enrollment in Guam was 28,000 and in Puerto Rico, 1,618,000. Some data for 2003 have been revised and differ from the previous edition of Health, United States. Data for additional years are available. See Appendix III.

SOURCES: InterStudy National Health Maintenance Organization Census. Annual Report on the Growth of HMOs in the U.S., 1984–1985 editions; The InterStudy Edge, 1990, vol. 2; The InterStudy Competitive Edge, Part II Managed Care Industry Report, 1991–2004. St. Paul, Minnesota (Copyrights 1985, 1990, 1991–2004: Used with the permission of InterStudy); Office of Health Maintenance Organizations: Summary of the National HMO census of prepaid plans—June 1976 and National HMO Census 1980. Public Health Service. Washington. U.S. Government Printing Office. DHHS Pub. No. (PHS) 80–50159; Population estimates used for calculations of regional percents from the U.S. Bureau of the Census at www​​/states/tables/NST-EST2004–08​.xls.

From: Trend Tables

Cover of Health, United States, 2005
Health, United States, 2005: With Chartbook on Trends in the Health of Americans.
National Center for Health Statistics (US) .
Hyattsville (MD): National Center for Health Statistics (US); 2005 Nov.

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