We conducted a study on 140 patients who sought advice at hospital after a non-occupational exposure. The full 28-day course of prophylactic antiretroviral therapy was completed by 109 patients. No HIV contamination was observed. Factors associated with suboptimal adherence were African ethnicity [odds ratio (OR) 13.3, 2.02-87.54] and oral sexual intercourse (OR 8.35, 1.66-41.99). Compliance with prophylactic antiretroviral therapy can be increased by addressing social and psychological barriers to adherence.