The nosological heterogeneity of catatonic schizophrenia was the focus of a family study involving 139 catatonic patients. The clinical dichotomization of catatonia into periodic catatonia and systematic catatonia revealed good inter-rater reliability and stability of the diagnoses at follow-up. Analysis of the cumulative morbidity risk among first-degree relatives gave an excessive familial aggregation of homogenous psychoses in periodic catatonia with a risk of 26.9%. The mode of inheritance was consistent with an autosomal dominant model. In contrast, first-degree relatives of probands with systematic catatonia had a morbidity risk of 4.6%. Subsequent investigations pointed to a potential association of systematic catatonia to exposure to midgestational infections in the index cases and linked these sporadic disorders to disturbances of fetal neurodevelopment. The periodic catatonia, an unequivocally genetically transmitted illness, is at present under investigation in a genome-wide linkage analysis.