We examined the impact of familial factors on age at onset in schizophrenia. Results from a literature review and from new analyses of two family studies and one twin study of schizophrenia support the following hypotheses: (1) no strong or consistent relationship exists between age at onset in schizophrenia and recurrence risk for schizophrenia in relatives; (2) age at onset in schizophrenia is not strongly related to the recurrence risk for other psychiatric disorders in relatives; and (3) in systematically ascertained pairs of affected siblings, the age at onset of schizophrenia is modestly correlated, whereas the correlation in age at onset in concordant monozygotic twin pairs is much higher. These results suggest that (1) from a familial perspective, early- and late-onset adult schizophrenia appear to be the same disorder, and (2) given that an individual will develop schizophrenia, familial factors, which may be genetic, influence the age at onset of the condition.