The potential for text messages to improve health outcomes in resource limited settings is still being explored. In South Africa, SMS text messages have been used to improve HIV health care service delivery by improving communication between patients and health personnel, and also as an appointment reminder. Two clinical trials in Kenya have evaluated the benefits of using mobile phone text message reminders to improve adherence to antiretroviral therapy. The WelTel trial reported improvements in adherence and viral load, a second reported an improvement in adherence and a reduction in treatment interruptions. A recent Cochrane systematic review summarized the evidence described in these two Kenyan trials. The WHO recommends more research on adherence to long-term therapies because poor adherence leads to poor health and increased health costs. However, the evidence on mobile phone text messaging to improve adherence to ART in developing countries is limited to one country. Given the importance of understanding the effectiveness of interventions to improve retention and adherence among people living with HIV in Africa, we conducted a randomized clinical trial to evaluate the utility of weekly motivational SMS texts on improving adherence and other important outcomes among a representative sample of HIV-positive adults in Cameroon. Our study did not find a significant effect of motivational SMS texts on improving adherence to ART over a 3 to 6 month period. This trial was unique in that it was the first to report the effect of an SMS intervention on ART adherence among treatment experienced patients in Africa. Two recent trials in Kenya demonstrated improved ART adherence among patients initiating ART, but used different intervention protocols. Our study had some important limitations. Firstly, our primary measures of adherence might have resulted in overestimates of the true adherence rate and the adherence reported for the last week may not adequately reflect adherence behaviors over longer periods because patients may become more adherent in the few days preceding their appointment. However, pharmacy refill data PI-103 PI3K inhibitor showed similar findings to self-reports. The trial design did not interfere with patient care by providing medication or lab tests so there are large amounts of missing data for CD4-positive-T-lymphocyte count and viral load. Drug stock-outs were also frequent in the last two months of the trial. This may explain why some participants missed their scheduled appointments. Previous studies conducted in the same parent population suggest that up to 25% have systematic reminder methods. Finally, our sample size was powered to detect a 20% difference in adherence between both arms. The difference we found was much less. Our findings should be interpreted in light of the published trials in Kenya, which show some improved adherence rates after twelve months, also reported in a Cochrane review synthesizing data from both trials. The interventions evaluated were somewhat different. While our trial used motivational messages, with the intention to produce a change in adherence behavior, and no compulsory feedback, the Weltel trial used a simple SMS inquiry on the participants’ health and was therefore interactive. The second trial used short and long one-way messages: the longer message with encouraging content, but no option for feedback. Even though we used optional feedback, we did not detect any improvements in adherence.