In attempt to investigate the relationship of birth rank and family size with the incidence of schizophrenic in an Iranian culture, case notes of 644 schizophernic patient as (432 males and 212 females) admitted to Roozbeh Hospital, University of Tehran were studied. The incidence of schizophrenic appeared to be significantly more frequent among the first-half position of birth orders in the families of 4 children and over; this being more marked in males than in females; and the first and second births comprising the lightest incidence of the illness.