The prevalence of obesity, a major chronic health problem that is an independent risk factor for coronary heart disease (CHD), continues to increase at an alarming rate. Although weight control research has significantly improved short-term treatment success, long-term weight loss maintenance has lagged behind. Research has demonstrated a consistent relationship between self-monitoring eating and physical activity habits and success in weight loss as well as in maintenance of weight loss. However, the methods primarily used for self-monitoring continue to be the paper diary (PD), which is time consuming and burdensome. Moreover, PDs do not permit immediate external feedback to support and motivate the individual. Emerging technologies could improve self-monitoring and weight loss treatment. However, the use of these technological advances, such as a personal digital assistant (PDA), has not been studied in weight loss treatment. The primary aim of this behavioral weight loss treatment study is to determine if self-monitoring of daily eating and physical activity habits using a PDA, with or without a tailored feedback intervention, is superior to using a PD in terms of promoting and maintaining short- and long-term weight loss. Secondary aims include comparing the effect of treatment group assignment on adherence to self-monitoring and on risk factors for CHD (lipids, glucose, insulin, C-reactive protein). We propose to enroll 198 subjects and randomize them to one of three treatment groups that will use different methods to self-monitor eating and physical activity habits: (1) use of the traditional PD with delayed written feedback, (2) use of a PDA with limited feedback on daily targets, or (3) use of a PDA with limited feedback on daily targets plus receive daily, subject-tailored feedback messages via the PDA. The proposed study includes prolonged (24 months) supervision of self-management with three important components: self-monitoring, feedback, and ongoing contact. Subjects will complete assessments at baseline, 6, 12, 18, and 24 months. This innovative study will provide information on the efficacy of combining technological advances with proven behavioral strategies.