The objective of the paper was to compare provider practices in prescribing antiretroviral (ARV) drug regimens and use of laboratory monitoring at three health care facilities and to determine whether Brazilian national guidelines are being followed. A retrospective, cross-sectional survey was employed. We selected a sequential sample of patients on ARV therapy who registered at three health care facilities in Rio de Janeiro, Brazil, during 2001. We abstracted 2001 patient visit data from medical records using standardized data forms. Provider practice was compared to the 2000 Brazil national guidelines for ARV use. Providers who prescribed recommended or acceptable regimens were considered as having conformed to guidelines. Only 2% of patient records (N=984) reported use of inappropriate regimens as defined by the Brazil 2000 national ARV guidelines. Forty-nine per cent of patients at the Evandro Chagas hospital, 17% of those at Hospital Geral, and 57% of those at Centro da Saude were prescribed recommended therapies. Twenty per cent of patients seen at the public district hospital received dual ARV therapy, an acceptable regimen at the time. Although the national guidelines do not provide recommendations on laboratory monitoring, during the 1 year study period a majority of patients had at least one CD4+ cell count (92%) or viral load measurement (86%). Providers' practices in prescribing ARV regimens at these Rio de Janeiro facilities conform to national guidelines. Physicians would benefit from Brazilian ARV guidelines which incorporate the international consensus on the frequency of laboratory monitoring appropriate for patients in resource-constrained settings.