Medication use is an essential element of healthcare, yet drugs can cause undesirable effects, making medication errors an important issue in hospitals. In antiretroviral therapy (ART), the diversity of regimes and protocols that require adjustment to the clinical situations of patients make drug use particularly challenging, given the possibility of drug interactions and the need for dose adjustments based on renal and hepatic function. Evaluating 565 prescriptions for 37 HIV/AIDS inpatients receiving ART in a teaching hospital, this descriptive, crosssectional study sought to identify opportunities for the engagement of pharmacists in advancing the rational use of drugs. The prescription errors identified were of three types: of administration (patient and prescriber identification, legibility, drug name, dosage form, and administration route), of dosage (concentration, dosage intervals, dose too high, dose to low, "as-needed" prescriptions, and information on dilution/reconstitution of prescribed drugs), and of therapy (medication contraindicated for the condition, duplicate therapy, and lack of dose adjustment for renal or hepatic function). For 7204 drugs prescribed, 5512 errors were identified: 41% of dosage, 40% of administration, and 19% of therapy. Preventive measures such as implementing electronic prescribing, along with the development of clinical pharmacy activities, are expected to contribute to the prevention of prescription errors.