Internetbased cognitive behavior therapy (iCBT) aimed att preventing relapse into major depression.

The control group in the study will fill out questionnaires every month and will be interviewed every month to detect any relapses. They will also receive feedback on there self-reported symptoms.

Internetbased cognitive behavior therapy (iCBT) contains interventions that will help the participant to change her behavior to experience more positive reinforcement in daily life and also to challenge her negative patterns of thought. There are also information and exercices to improve sleep, increase physical activity, train mindfulness, handle anxiety and to learn about depression.

The total number of days that a participant has been absent from work due to sick leave (any cause). Data will be collected from the National Insurance Agency at the end of the study.

Self-reported number of sick leave days during the study will be collected cumulatively every month during the study time and summarised after 24 months.

Change in diagnostic status (depressive relapse) will be assessed in a telephone interview every month during the study. The definition of a relapse is to fulfill the diagnostic criteria for major depression according to the DSM-IV at any time after the study start.

Change in depressive symptoms will be measured by an internetbased version of the Montgomery-Asberg Depression Rating Scale - Self rated. The patient will fill out the questionnaire every month.

Health related quality of life will be measured by an internetbased version of the EQ-5D. The questionnaire will be filled out every month.