Mobile Health (mHealth) interventions have become effective strategies to increase adherence to antiretroviral treatment (ART) in people living with HIV (PLWH). mHealth interventions use phone calls, e-mails, smartphone apps or short text messages (SMS) as reminders of medical appointments or ART adherence. SMS are a highly accepted mHealth strategy. Systematized processes to validate SMS tailored to end-user preferences are required to increase the effectiveness of mHealth interventions. We describe a structured approach to develop a set of SMS tailored to Mexican HIV+ individuals, focused on improving ART adherence and healthcare appointments. The process included three sequential phases: SMS design by HIV-healthcare professionals, validation by expert referees, and testing by PLWH. A set of 108 SMS in four categories (motivational self-healthcare messages, ART-collection, medical and laboratory-appointment reminders) was designed. Expert referees assessed 94.5% of messages as adequate, 65.7% as useful. Seventy-one SMS were further tested by PLWH, who considered 100% of SMS to be understandable and 57.7% useful. SMS had adequate intra-judge agreement scores for clarity and acceptability (ICC-2 = .08-.49). Qualitative feedback from expert referees and PLWH was incorporated into SMS. A final set of 41 highest-rated SMS was obtained. Careful validation of SMS could increase the effectiveness of mHealth interventions.