Objective To assess whether a warning system based on mobile SMS messages increases the adherence of HIV-infected Brazilian women to antiretroviral drug-based treatment regimens and their impressions and satisfaction with respect to incoming messages. Design A randomized controlled trial was conducted from May 2009 to April 2010 with HIV-infected Brazilian women. All participants (n = 21) had a monthly multidisciplinary attendance; each participant was followed over a 4-month period, when adherence measures were obtained. Participants in the intervention group (n = 8) received SMS messages 30 min before their last scheduled time for a dose of medicine during the day. The messages were sent every Saturday and Sunday and on alternate days during the working week. Participants in the control group (n = 13) did not receive messages. Measurements Self-reported adherence, pill counting, microelectronic monitors (MEMS) and an interview about the impressions and satisfaction with respect to incoming messages. Results The HIV Alert System (HIVAS) was developed over 7 months during 2008 and 2009. After the study period, self-reported adherence indicated that 11 participants (84.62%) remained compliant in the control group (adherence exceeding 95%), whereas all 8 participants in the intervention group (100.00%) remained compliant. In contrast, the counting pills method indicated that the number of compliant participants was 5 (38.46%) for the control group and 4 (50.00%) for the intervention group. Microelectronic monitoring indicated that 6 participants in the control group (46.15%) were adherent during the entire 4-month period compared to 6 participants in the intervention group (75.00%). According to the feedback of the 8 participants who completed the research in the intervention group, along with the feedback of 3 patients who received SMS for less than 4 months, that is, did not complete the study, 9 (81.81%) believed that the SMS messages aided them in treatment adherence, and 10 (90.90%) responded that they would like to continue receiving SMS messages. SMS messaging can help Brazilian women living with HIV/AIDS to adhere to antiretroviral therapy for a period of at least 4 months. In general, the results are encouraging because the SMS messages stimulated more participants in the intervention group to be adherent to their treatment, and the patients were satisfied with the messages received, which were seen as reminders, incentives and signs of affection by the health clinic for a marginalized population.