BACKGROUND Anemia is common in HIV infection, particularly in advanced disease states. We wished to determine how highly active antiretroviral therapy (HAART) and other factors affected the level of hemoglobin in HIV infection. METHODS We analyzed data from 905 patients receiving care at Johns Hopkins in Baltimore, Maryland after July 1, 1996. Analyses were done of hemoglobin levels obtained at baseline and during 1 year of follow-up in patients who received and did not receive a HAART regimen. Use of HAART and other demographic and clinical factors were examined. RESULTS Eleven percent of patients had a hemoglobin count <10 g/dL, 27% had a hemoglobin count 10 to 12 g/dL, and 21% had a hemoglobin count of >14 g/dL at baseline before HAART was started. During 1 year of follow-up, use of HAART was associated with a hemoglobin levels >14 g/dL in 42% of patients, irrespective of use of zidovudine as part of HAART regimen, compared with 31% of patients who did not use HAART. In multivariate analysis, use of HAART was strongly associated with not having anemia during 1 year of follow-up, adjusting for patient gender, race, injection drug use history, baseline CD4 and HIV-1 RNA levels, and anemia treatments. CONCLUSIONS HAART is an effective treatment of the anemia of HIV infection. Patients who continue to have symptomatic anemia while receiving HAART may need additional intervention.