[The American health care system: origins and developments of managed care organizations].

The first Health Maintenance Organizations (HMOs) appeared in the 70's in the context of care rationing. These organizations have rapidly become responsible for delivering care to the general population. Cost/effectiveness studies and other quality control programs rapidly appeared, followed by other sophisticated cost-control devices. The following article gives information on the current difficulties encountered by HMOs. Other aspects of the care given by the HMOs are also addressed. The economical and legal difficulties to which these companies were confronted have prompted them to withdraw from some market segments. Patients have become more vulnerable, despite limited attempts of reforms.