This study describes use of medical, mental health, alcohol, and drug services by 832 adult residents of the New York City homeless shelter system and examines associations between service use during the past three months and an array of predisposing, enabling, and need factors. Utilization rates were 23% for medical services, 13% for mental health services, and 10 and 7.5% for alcohol and drug treatment services, respectively. Service contacts were more often hospitals than ambulatory care clinics. Logistic regression analyses revealed that need factors were stronger predictors of all four types of service use. Predisposing factors other than education and black ethnic status were not significant, and the enabling factor of enrollment in Medicaid and/or Medicare was significant only for use of medical and drug services. Among the need factors, measures of mental health status were analyzed as indices of distress to test a stress-utilization model of prediction for all four types of service use. While these measures did not predict use of nonmental health services, physical health problems were associated with use of all four types of services. Implications for future health services research and for service delivery to the homeless are discussed, including the need for more information on availability of services and on psychosocial and cultural characteristics of homeless persons that may affect their help-seeking behavior.