OBJECTIVE: The aim of this paper was to review the clinical and conceptual implications of the studies investigating prodromal symptoms of mania, depression, and panic disorder. METHOD: Twenty-four studies specifically addressing the issue of prodromal symptoms in mood and anxiety disorders were selected by computer search (Medline) and manual search of Index Medicus and the psychiatric literature. RESULTS: Most of the studies have described a prodromal phase in the development of mania, depression, and panic attacks. CONCLUSIONS: The appearance of prodromal symptoms may precede the full syndrome by weeks or months; if these symptoms are detected, recurrences of affective disorders (bipolar illness, unipolar depression, panic disorder) could be treated earlier and perhaps more effectively. DSM-III has emphasized the traditional clinical syndromes and cross-sectional descriptions. Appraisal of prodromal and residual phases may complement this approach. The longitudinal study of prodromes, the fully developed disorder, and residual states calls for an assessment of personality, neurotic traits, and their interaction in the evolution of affective disorders.