BACKGROUND Since many successful dieters regain the weight they lose, programs that teach maintenance skills are needed. We developed a maintenance program based on self-regulation theory and tested the efficacy of delivering the program face to face or over the Internet. METHODS We randomly assigned 314 participants who had lost a mean of 19.3 kg of body weight in the previous 2 years to one of three groups: a control group, which received quarterly newsletters (105 participants), a group that received face-to-face intervention (105), and a group that received Internet-based intervention (104). The content of the programs in the two intervention groups was the same, emphasizing daily self-weighing and self-regulation, as was the frequency of contact with the groups. The primary outcome was weight gain over a period of 18 months. RESULTS The mean (+/-SD) weight gain was 2.5+/-6.7 kg in the face-to-face group, 4.7+/-8.6 kg in the Internet group, and 4.9+/-6.5 kg in the control group, with a significant difference between the face-to-face group and the control group (2.4 kg; 95% confidence interval [CI], 0.002 to 10.8; P=0.05). The proportion of participants who regained 2.3 kg or more over the 18-month period was significantly higher in the control group (72.4%) than in the face-to-face group (45.7%; absolute difference, 27%; 95% CI, 14 to 39; P<0.001) or the Internet group (54.8%; absolute difference, 18%; 95% CI, 5 to 30; P=0.008). Daily self-weighing increased in both intervention groups and was associated with a decreased risk of regaining 2.3 kg or more (P<0.001). CONCLUSIONS As compared with receiving quarterly newsletters, a self-regulation program based on daily weighing improved maintenance of weight loss, particularly when delivered face to face. (ClinicalTrials.gov number, NCT00067145 [ClinicalTrials.gov].)