OBJECTIVE: The purpose of this study was to assess the effect of psychiatric comorbidity on specific measures of hospital utilization, including length of stay, among hospitalized AIDS patients. METHOD: Data collection involved medical record abstraction for AIDS patients admitted to any one of 19 hospitals in Washington State during 1990. Psychiatric comorbidity was defined by the presence of an ICD-9 code reflecting psychiatric illness. Medical/surgical admissions of AIDS patients with psychiatric diagnoses were compared to those of AIDS patients without psychiatric diagnoses on measures of mean length of stay for the first admission in 1990, total number of hospitalizations in 1990, and total number of hospital days in 1990. Medical morbidity was addressed using CD4+ cell count and current and previous AIDS- defining illnesses as markers of disease severity. RESULTS: Of 357 patients hospitalized with AIDS, 49 (14%) had at least one psychiatric diagnosis. Patients with psychiatric illness were hospitalized an average of 6.6 days longer than AIDS patients without such illnesses. Differences in medical morbidity did not account for the longer length of stay. CONCLUSIONS: Psychiatric comorbidity increased the average length of stay among hospitalized AIDS patients. Future research needs to address the possible effects of this phenomenon on quality and cost of care received by AIDS patients.Abstract Teaser