Considerable evidence suggests that people with HIV disease are significantly more distressed than the general population, yet psychiatric disorders are commonly under-detected in HIV care settings. This study examines the prevalence of three stress-related psychiatric diagnoses--depression, posttraumatic stress disorder (PTSD), and acute stress disorder (ASD), among a vulnerable population of HIV-infected patients. Among approximately 350 patients attending two county-based HIV primary care clinics, 210 participants were screened for diagnostic symptom criteria for depression, PTSD, and ASD. Standardized screening measures used to assess for these disorders included the Beck Depression Inventory, the Posttraumatic Stress Checklist, and the Stanford Acute Stress Questionnaire. High percentages of HIV-infected patients met screening criteria for depression (38 per cent), PTSD (34 per cent), and ASD (43 per cent). Thirty eight percent screened positively for two or more disorders. Women were more likely to meet symptom criteria for ASD than men (55 per cent vs. 38 per cent, OR=1.94, CI95 per cent=1.1-3.5). ASD was detected more commonly among African-American and white participants (51 per cent and 50 per cent respectively), compared with other ethnic groups. Latinos were least likely to express symptoms of ASD (OR=0.52, CI95 per cent=0.29-0.96). Of the 118 patients with at least one of these disorders, 51 (43 per cent) reported receiving no concurrent mental health treatment. Patients with HIV/AIDS who receive public healthcare are likely to have high rates of acute and posttraumatic stress disorders and depression. These data suggest that current clinical practices could be improved with the use of appropriate tools and procedures to screen and diagnose mental health disorders in populations with HIV/AIDS.