The use of mobile health (mHealth) technologies addressing HIV disparities among gay, bisexual, and other men who have sex with men (GBMSM) has increased. A systematic review of mHealth interventions for HIV prevention and treatment among GBMSM was conducted to summarize the current evidence and provide recommendations for future research. PRISMA guidelines were followed (PROSPERO ID: 148452). Studies identified via PubMed, PsychInfo, or Embase were included that (i) were in English, (ii) were published in a peer-reviewed journal prior to July 1, 2019, (iii) presented primary results, (iv) included only GBMSM, and (v) reported the results of an mHealth intervention (e.g., text message, phone/mobile application [app]) to improve HIV prevention or treatment outcomes. Of 1,636 identified abstracts, 16 published studies met inclusion criteria. Eleven studies were conducted in the United States. One study was a fully powered randomized controlled trial (RCT), seven were single-arm pilots with pre-post assessments, four were pilot RCTs, and four tested public health campaigns with post-assessments. Seven developed study-specific apps, five used text messaging, and four used existing social networking apps. Most (81%) targeted prevention outcomes. Nine cited a specific behavioral theory. All studies found that a mHealth approach was feasible and acceptable. All interventions provided evidence of preliminary efficacy or promising trends on primary outcomes. Although mHealth interventions for HIV prevention and treatment appear feasible and acceptable, most published studies are small pilot trials. Additional research assessing the efficacy and mechanisms of mHealth interventions is needed.