After pointing to the heterogeneous results of past investigations into the genetics of catathymic delusional illnesses we present our own findings. By grouping the primary probands according to their psychopathology we showed that the relatively few schizophrenic secondary probands are fairly equally distributed over all the subgroups of the case material, whereas the relatively frequent manic depressive secondary probands are related exclusively to those primary probands whose general psychiatric symptomatology, irrespective of the catathymic delusional syndrome, was classified psychopathologically as manic-depressive.