BackgroundSub-threshold depression is a prognostic variable for major depression. Interventions in sub-threshold depression may prevent the onset of new cases of major depression.AimsTo examine the effects of minimal-contact psychotherapy in primary care patients with sub-threshold depression on the onset of major depression, on the reduction in depressive symptoms and on health-related quality of life.MethodWe conducted a randomised trial in primary care, in which patients screened for sub-threshold depression were randomly assigned to minimal-contact psychotherapy (n=107) or to usual care (n=109).ResultsOne year after baseline, the incidence of major depressive disorder was found to be significantly lower in the psychotherapy group (12%) than in those receiving usual care (18%). Small but significant effects were also found on depressive symptoms and on aspects of health-related quality of life.ConclusionsPrimary care patients with sub-threshold depression can benefit from minimal-contact psychotherapy.