The hypothesis that mothers of winter–spring-born schizophrenics have an unusual pattern of conception which results in an excess of winter–spring births was tested by studying the distribution of birth-dates of 401 siblings of 120 winter–spring-born schizophrenics and 157 siblings of 59 winter–spring-born controls. All analyses were gender-specific. The results suggest there is no association between the probability of a winter–spring date of birth and being a sibling of a winter–spring–born schizophrenic or control.