A possible association between birth order and schizophrenia has been sought by a number of investigators. The question considered as early as 1916 by Rüdin has not been resolved satisfactorily since; late birth order has been indicated in some samples of patients (e.g. Granville-Grossman, 1966; Schooler, 1964), early birth order in others (e.g. Solomon and Nuttall, 1966; Sundararaj and Rao, 1966) and an absence of any birth order effect has been reported for still other samples (e.g. Burton and Bird, 1963; Gregory, 1959; Smith and McIntyre, 1963).