The typical course of Brief and Acute Psychoses has been described as remitting and relapsing. This is true for most historical predecessors of what we today call Acute and Transient Psychoses, especially for the cycloid psychoses which are believed to occur in recurring episodes, interrupted by symptom-free intervals. Leonhard (1957) found the duration of episodes in cycloid psychoses shorter than in manic-depressive illness and a lower number of episodes over the whole course of illness. The relatively short duration of cycloid episodes was confirmed by most later investigators (Kirov, 1972; Perris, 1974; Kimura et al., 1980; Bräunig and Fimmers, 1995).

The duration of the cycle, i.e. the period of time comprising an illness episode and the ensuing interval, was reported by Perris (1974) with a mean of 2 years, but about twice that long between the first two episodes. This is similar to affective and schizoaffective disorders – both unipolar and bipolar (Angst et al., 1980; Marneros et al., 1989b, 1991b; Angst and Preisig, 1995). A further reduction of cycle length during long-term course as known for bipolar affective and schizoaffective psychoses was not identified by Perris in his data (1974). Kirov in his series of cycloid psychoses, found a free interval between two episodes of 20.3 months (Kirov, 1972). Of a similar order of magnitude are the findings of Cutting (1978), who found a relapse rate of 0.28 episodes/year, and those of Bräunig (1995), who reported an average of 3 episodes per year.