Deficit and non-deficit subtypes were examined for their concordance in 83 sibling pairs of 109 schizophrenic patients belonging to 46 multiply affected families. Using a sib-pair method, we have found that the distribution of deficit and non-deficit syndromes in sibling pairs of schizophrenic patients differed significantly from chance expectation. This familial aggregation suggests that the syndrome may be used to define phenotypes for genetic studies.