The design of the study is a complex intervention study with a multi-method design, consisting of a quasi-experimental trial and a qualitative study. The sample will be drawn from schools in Oslo. Overweight adolescents will be selected and placed in the intervention group or control group respectively. The sampling will be based on objective measures of weight and height and using Cole's index to define overweight and obesity. Weight and height will be measured by the school nurse and will be coordinated with her regular meetings with the adolescents in 8th grade.. The study group will receive the web-based intervention and the control group will receive standard care. At baseline, 3 months and 1 year both the experimental group and the control group will be measured at relevant variables. In the qualitative part of the study, in depth interviews with the adolescents in the intervention group will be performed and they will write daily unstructured blogs on the web. The sampling procedure for the qualitative part of the study will follow the sampling procedure of the intervention study. From the intervention group, a strategic or purposive sample of adolescents will be asked to participate in the qualitative part (Gerrish and Lacey 2006). A sample of maximum variation according to gender and sosio-demographic variables is intended. Sampling continues until saturation is reached and the adolescents will be interviewed in depth before the intervention starts, further at 3 and 12 months after the intervention is ended.