Winter birth is a widely replicated risk factor for schizophrenia. However, previous studies have suggested that patients with the deficit syndrome of schizophrenia have an excess of summer births. We tested the summer birth effect in a population-based study. Data came from the Epidemiological Catchment Area study, which had a representative sample of the U.S. population. Psychotic patients with features of the deficit syndrome had a significant association with summer birth, compared with the general population. There was also a significant association between summer birth and the deficit syndrome within the psychotic population, after accounting for the variance due to disorganization, hallucinations and delusions, and demographic characteristics. These findings add to the evidence suggesting the etiopathophysiology of the deficit group differs from that found in other patients with schizophrenia.