To inform ethical procedures for human subjects research using mobile health, we examined perceived risks and benefits of study participation among emerging adults with drug use who completed text message assessments of substance use and sexual behaviors. Most participants reported comfort with participation and some reported perceived benefits, such as improved relationships. Perceived risks were infrequently reported, including negative emotions and legal or financial concerns. In conclusion, participants from a vulnerable population reported few perceived harms of participation in longitudinal mHealth (...) assessments of sensitive behaviors. Researchers should continue characterizing participants’ perspectives on ethical aspects of mHealth research. (shrink)