Summary1) One hundred and thirty four endogenous manic‐depressive psychotics were classified into 24 types according to the combination of the age of onset (early, intermediate, middle, late) and length of symptom‐free interval period (continuous, frequent, periodic, periodic to continuous, periodic to frequent, intermittent).2) The cases with shorter symptom‐free interval period such as those belonging to continuous and frequent types tended to have earlier onset, and longer interval tended to be combined with later onset.3) The incidence of bipolar type was very high in the early onset group and declined as the age of onset became higher. All of the continuous type patients showed bipolar course, whereas the incidence of monopolar type was 4 to 5 times as high as that of bipolar in periodic and intermittent types.4) The incidence of episodes with precipitating factors was around 70% in all types except for a very low incidence in the early‐continuous type. However, the number of cases in which more than a half of their episodes were precipitated by external factors, was only about 30% of the cases with precipitating factors. The incidence of such cases was very low in continuous and frequent types and relatively high in periodic and intermittent types.5) The incidence of the episode with precipitating factors was highest in the first episode and declined progressively as the episode repeated. That is, the disease tended to recur automatically without discernible precipitating factors supposedly due to a mechanism of channelling.6) No definite relationship could be found between the personality types such as immodithymic (immobilithymic, melancholic) and cyclothymic types, the onset‐interval types, and the presence or absence of precipitating factors, except for a low incidence of immodithymic personality in continuous type.7) The role of the biological process, premorbid personality and external precipitating factors in the pathogenesis of affective