Patients and the public could benefit from identification of factors that prevent drug users' heavy reliance on inpatient care; however, optimal health care delivery models for illicit drug users remain ill-defined. To evaluate associations of outpatient medical and drug abuse care with drug users' subsequent hospitalization rates. Retrospective cohort study of data from longitudinally linked claims for all ambulatory physician/clinic services and drug abuse services covered by the New York State Medicaid program. A total of 11 556 human immunodeficiency virus (HIV)-positive and 46 687 HIV-negative drug users. Hospitalization in federal fiscal year (FFY) 1997 compared by 4 patterns of care in FFY 1996: regular drug abuse care (>/=6 months in 1 program), regular medical care (>35% of care from 1 clinic, group practice, or individual physician), both, or neither. Hospitalization occurred in 55.6% of HIV-positive and 37.5% of HIV-negative drug users, with a mean of 27.5 and 24.5 inpatient days, respectively. In HIV-positive drug users, the adjusted odds ratio (AOR) for hospitalization was lowest among those with both regular medical and drug abuse care (AOR, 0.76; 95% confidence interval [CI], 0.67-0.85) followed by those with regular medical care alone (AOR, 0.82; 95% CI, 0.74-0.91) and regular drug abuse care alone (AOR, 0.85; 95% CI, 0.76-0.96) vs those with neither. In HIV-negative drug users, the AOR of hospitalization was lower for those with regular medical and drug abuse care (AOR, 0.73; 95% CI, 0.68-0.79), regular drug abuse care alone (AOR, 0.71; 95% CI, 0.66-0.76), and regular medical care (AOR, 0.91; 95% CI, 0.86-0.95) vs those with neither. Both types of care showed favorable effects for all but drug abuse-related hospitalizations. Our data indicate that regular drug abuse care with regular medical care for drug users is associated with less subsequent hospitalization.