INTRODUCTION: The reasons why research participants join clinical trials remains an area of inquiry especially in low and middle income countries. METHODS: We conducted exit interviews with participants who took part in a trial which aimed to evaluate whether long term prophylaxis with cotrimoxazole can be safely discontinued among adults who have been stabilised on antiretroviral therapy (ART). Participants were all reported to be stable on ART and had been participating in the trial for between 12 and 36 months; at the end of the trial participants were interviewed using a semi-structured questionnaire. One of the objectives of the exit interview was to find out what motivated the participants to join the research. RESULTS: Participants gave personal reasons for joining the trial, frequently linked to their health and well-being as well as reduction of pill burden. CONCLUSION: We conclude that underlying reasons for joining clinical trials may extend beyond or can be different from the rationale given to the participants before enrolment by the research team. The reasons that motivate enrolment to clinical trials and research in general require further investigation in different settings. TRIAL REGISTRATION NUMBER: ISRCTN44723643.