After several years of nationwide study, a significant experiment in group practice under a voluntary prepayment plan, which was launched in New York in March 1947, is revealing an extraordinary amount of hitherto unavailable information concerning the utilization of medical services by a completely insured population. ORGANIZATION The Health Insurance Plan of Greater New York is a community-sponsored, voluntary medical care plan incorporated under the New York State Insurance Law as a nonprofit agency. It is not intended to be merely another medical insurance company. Its purpose is to provide comprehensive medical services to workers and their families through medical teams which assume full responsibility for medical care of the group in return for distribution of the premium income in the form of capitation payments. It was hoped that in this manner comprehensive medical care—preventive, early diagnostic and curative—could be provided on a sound financial and actuarial basis and without