Studied the prevalence of mental disorders in age, sex, and class groups in Egyptian society, attempting to find plausible explanations for disproportionate prevalence of different mental disorders in Egyptian social groups, and to establish a basis for comparing Western and non-Western mental disease incidence. It was found that (a) the clinical clusters of behaviors that provide the basis for Western nosology occurred in Egypt; (b) Egyptian symptom content was different from that in Europe and America; (c) interclass differences were crucial for symptom content; (d) more males than females were schizophrenic; (e) more serious cases of psychopathology were found among females; (f) a disproportionate percentage of hospitalized cases consisted of young adults; (g) organic reaction types were rare; and (h) prevalence of mental disorders was greatest among the lower classes. The discussion offers cultural interpretations for the findings, notes problems in interpretation, and identifies needs for better diagnosis of schizophrenia.