This review of the literature on the importance of congruence of mood to identify nosological sub-categories among the affective disorders showed the limited value of this concept. The reported prevalence rates of affective psychoses with mood-congruent, mood-incongruent and a combination of these symptoms vary widely among the different studies. This categorization seems neither to identify sub-groups with distinct demographic and onset characteristics nor to predict course and outcome. Furthermore, the ambiguity of the guidelines and the different use of this concept in the studies increase the confusion. The only heuristic value of the use of this concept seems to be its prediction of change of diagnosis. The authors suggest eliminating the concept of mood congruence from the categorization of affective disorders and, if not, to state more concise and explicit guidelines for research and clinical use.