SETTING: Thyolo, rural southern Malawi. OBJECTIVES: To determine 1) the proportion who continue with cotrimoxazole prophylaxis for the prevention of opportunistic infections, and 2) the reasons for continuing or stopping prophylaxis, in human immunodeficiency virus (HIV) infected individuals with tuberculosis (TB) who complete anti-tuberculosis treatment. DESIGN: A cross-sectional study. METHODS: A questionnaire study of all HIV-infected TB patients who had been registered over a 3-month period to receive anti-tuberculosis treatment and cotrimoxazole prophylaxis and who had completed antituberculosis treatment 3-6 months earlier. RESULTS: Of 82 HIV-infected individuals who were alive at the time of interview, 76 (93%) were continuing with cotrimoxazole and wished to do so indefinitely. The most common reason for continuing the drug was to prevent illness associated with HIV, while the most common reason for stopping was long distances to the health facility. Ninety-six percent of patients received cotrimoxazole free of charge from a health centre. Of those who wished to continue indefinitely, the majority (63%) could not afford to pay for the drug. CONCLUSIONS: In a rural setting, the great majority of HIV-infected individuals continued with cotrimoxazole after completing anti-tuberculosis treatment. Making the drug available and providing it free of charge is essential if it is to remain accessible for longer term prevention.