Background. The concept of duration of untreated psychosis (DUP) has recently attracted much interest because of its possible relationship to treatment outcome and implications for preventive efforts with reference to psychotic disorders, especially schizophrenia. In this paper we review critically the literature concerning the concept and its importance.

Methods. Articles concerned with measuring DUP and those that have been suggested to provide indirect or direct evidence of the effect of DUP on treatment outcome are reviewed.

Results. Evidence thus far suggests that DUP may be related to ease of reducing psychotic symptoms once treatment begins for first episode patients, but there is no evidence of a relationship to likelihood of relapse. There has been little investigation of the relationship of DUP to other long-term outcomes such as negative symptoms and cognitive functioning neither have the possible confounds of DUP been widely investigated or controlled.

Conclusions. It is important that there should be more thorough investigations of DUP, its correlates, and the extent to which it does mediate any advantages of earlier intervention.