Inpatient use data were examined for fiscal years 1999-2001. Patients with and without psychiatric diagnoses were compared for length of hospital stay and complexity of illness. Patients with psychiatric disorders represented 33%-35% of total cases. Substance use (9,824 cases), mood disorders (2,524 cases), and cognitive disorders (2,362 cases) were the most common psychiatric illnesses. Patients with substance use disorders or no psychiatric diagnosis had the shortest adjusted length of stay, whereas the small number with adjustment disorders (N=147) had the longest. Other psychiatric patients had lengths of stay between these extremes. Excepting substance use disorders, increased lengths of stay with psychiatric comorbidity have persisted into the managed care era.