TITLE: Mobile Phone Adherence Support for HIV Patients in Manila, Philippines BACKGROUND: In the context of a rapidly accelerating HIV epidemic in the Philippines concentrated among men who have sex with men (MSM), behavioural interventions to support delivery of HIV care and treatment are needed. Mobile health (mHealth) interventions have potential to improve adherence to HIV medicines but have not been implemented or evaluated in this setting. METHODS: This thesis examines the development, implementation, and evaluation of a mobile phone intervention to support adherence to antiretroviral therapy for people living with HIV in Metro Manila, Philippines. The behavioural science-informed, user-informed approach to intervention development is described. A mixed methods process evaluation assesses the intervention’s feasibility, acceptability, and fidelity of delivery. A prospective cohort study documents the adherence to antiretroviral therapy and demographic, behavioural, and clinical characteristics of the 462 participants. RESULTS: The intervention consisted of a menu of services (pill reminders, health tips, appointment reminders, and adherence feedback) that could be delivered by voice call or text message on the days and at times chosen by the user. Factors negatively associated with adherence were longer time on ART, inconsistent condom use, and substance use. Being in a relationship was positively associated with adherence to ART. While the intervention was acceptable, fidelity of delivery was poor due to technological challenges related to the telecommunications provider. Improved adherence over time was observed, with the proportion of patients taking more than 95% of their ART doses increasing from 78.6% at baseline to 90.3% at 48 weeks. Viral load suppression rates did not change significantly over the course of the study. Neither adherence nor viral load was associated with exposure to the intervention. CONCLUSION: Evidence regarding the efficacy of mobile phone interventions to support adherence to ART remains mixed. Interventions to support Filipino MSM living with HIV should incorporate elements that focus on social support and harm reduction for substance use.