Lactic acidosis has been described in persons with HIV infection particularly in association with the use of nucleoside reverse transcriptase inhibitors (NRTIs). Little is known about the epidemiology of this problem. We reviewed the records of all HIV-infected adults with elevated lactate levels admitted to Barnes-Jewish hospital from 1996 to 1998. There were 37 patients identified with elevated lactate levels. The annual rate of elevated lactate levels was 22.6, 33.9, and 30.8 per 1,000 admissions in 1996, 1997, and 1998, respectively. The median age of the patients was 40.4 years; median CD4+ count was 148 cells/mm3; and the median HIV-1 RNA level was 4,401 copies/ml. The median lactate level was 4.5 mmol/liter (range, 2.2-19 mmol/liter). Twenty-nine patients (78%) had elevated lactate levels at admission. Elevated lactate levels were associated with sepsis (48.7%), pancreatitis (13.5%), liver failure (8.1%), multiorgan failure (8.1%), and other conditions. Five patients had lactic acidosis associated with the use of antiretroviral medications; one patient with unexplained lactic acidosis and four patients with pancreatitis. The mortality rate was 45.9% (17/37). Higher lactate levels were associated with increased mortality. In conclusion, elevated lactate levels were uncommon but not rare in hospitalized patients with HIV infection. Sepsis was the most commonly associated condition and antiretroviral medications were the second most frequently associated factor. There was no significant increase in the annual rate of lactic acidosis during this 3-year period.