Background. The aim of this review was to survey the available literature on prodromal and residual symptoms of unipolar major depression and bipolar disorder.

Methods. Both a computerized (Medline) and a manual search of the literature were performed.

Results. In a substantial proportion of patients with affective disorders a prodromal phase can be identified. Most patients report residual symptoms despite successful treatment. Residual symptoms upon remission have a strong prognostic value. There appears to be a relationship between residual and prodromal symptomatology (the rollback phenomenon).

Conclusions. Appraisal of subclinical symptomatology in mood disorders has important implications for pathophysiological models of disease and relapse prevention. In depression, specific treatment of residual symptoms may improve long-term outcome, by acting on those residual symptoms that progress to become prodromes of relapse. In bipolar disorder, decrease of subclinical fluctuations and improvement of level of functioning by specific therapeutic strategies may add to the benefits provided by lithium prophylaxis.