The purpose of this study was to evaluate the effects of a mobile app designed to improve chronic disease self-management in patients aged 40 years and older with low health literacy and who had at least one chronic health condition, and to assess the impact of delivering information at different levels of reading difficulty. A randomized controlled trial was completed at two sites. Individuals aged 40 years and older screened for low health literacy who had at least one chronic health condition were randomly assigned to a tailored information multimedia app with text at one of three grade levels. Four primary outcomes were assessed: patient activation, chronic disease self-efficacy, health-related quality of life, and medication adherence. All groups showed overall increases in activation, self-efficacy, and health-related quality of life, but no change in medication adherence. No between-group differences were observed. The mobile app may have been effective in increasing participants’ levels of several psychosocial variables, but this interpretation can only be advanced tentatively in light of the lack of control-experimental group differences. Reading difficulty level was not significantly related to outcomes.