Aspects of the course of manic depressive and schizo-affective psychoses with high recurrence (the patient must have suffered from at least three episodes) are measured by length of episodes, intervals, and cycles. Differences between two patient samples from Switzerland and Poland, and differences between the two diagnostic groups are analyzed taking into account some independent variables such as sex, marital state, age at onset, precipitation, and symptomatology. Bipolar and schizo-affective psychoses show similar patterns of course: early onset, high relapse rate, high number of episodes, and short intervals. Compared to schizo-affective psychoses bipolar psychoses tend to have a higher frequency of episodes per year, shorter intervals, and the length of episodes is longer. Multivariate analysis shows very few correlations of independent variables with aspects of the course. On the whole the differences between the diagnostic groups are much smaller than between the two centers. The Polish and Swiss patient samples differ in course considerably. The patients from Zurich show longer episodes, intervals, and cycles, therefore, the frequency of episodes per year is lower in Zurich. Only a smaller part of the variance can be explained by differences in psychopathology (the Polish patients are more manic and more paranoid). There remain unexplained qualitative differences between the two centers which show how difficult it is to compare scientific results from different sources.