With the rapid adoption of mobile devices, mobile health (mHealth) offers the potential to transform health care delivery, especially in the world's poorest regions. We systematically reviewed the literature to determine the impact of mHealth interventions on health care quality for non-communicable diseases in low- and middle-income countries and to identify knowledge gaps in this rapidly evolving field. Overall, we found few high-quality studies. Most studies narrowly focused on text messaging systems for patient behavior change, and few studies examined the health systems strengthening aspects of mHealth. There were limited literature reporting clinical effectiveness, costs, and patient acceptability, and none reporting equity and safety issues. Despite the bold promise of mHealth to improve health care, much remains unknown about whether and how this will be fulfilled. Encouragingly, we identified some registered clinical trial protocols of large-scale, multidimensional mHealth interventions, suggesting that the current limited evidence base will expand in coming years.