Objective: To examine acceptability, attrition, adherence, and preliminary efficacy of mobile phone short message service (SMS; text messaging) for monitoring healthful behaviors in children. Design: All randomized children received a brief psychoeducational intervention. They then either monitored target behaviors via SMS with feedback or via paper diaries (PD) or participated in a no-monitoring control (C) for 8 weeks. Setting: University of North Carolina at Chapel Hill. Participants: Fifty-eight children (age 5-13) and parents participated; 31 completed (SMS: 13/18, PD: 7/18, C: 11/22). Intervention: Children and parents participated in a total of 3 group education sessions (1 session weekly for 3 weeks) to encourage increasing physical activity and decreasing screen time and sugar-sweetened beverage consumption. Main Outcome Measures: Treatment acceptability, attrition, and adherence to self-monitoring. Analysis: Descriptive statistics and nonparametric tests were used to analyze differences across time and group. Results: Children in SMS had somewhat lower attrition (28%) than both PD (61%) and C (50%), and significantly greater adherence to self-monitoring than PD (43% vs 19%, P less than 0.02). Conclusions and Implications: Short message service may be a useful tool for self-monitoring healthful behaviors in children, although the efficacy of this approach needs further study. Implications suggest that novel technologies may play a role in improving health. (Contains 3 tables.)