Mobile phones may provide a useful and engaging platform for supporting therapeutic services working with adolescents. This paper examines the potential benefits of the mobile phone for self-charting moods in comparison to existing methods in current practice. The paper describes a mobile phone application designed by the authors which allows adolescents to record moods on their personal mobile phones. The authors propose that a personal mobile device is more suitable for adolescents than other devices. A pilot study with a non-clinical adolescent group in schools comparing a mobile and a paper diary is presented, along with discussion and analysis of the results. The main finding of the study was that compliance was significantly higher on mobile phones than paper, and the task was not found to be any more difficult to complete using mobile phones than with paper charts. A number of salient issues requiring further research are also identified. (Contains 3 figures.)