ALTHOUGH A family history of schizophrenia is the best established risk factor for the disease,1 it may account for only a small proportion of the population occurrence of schizophrenia.2,3 Other factors, such as urbanicity at birth and upbringing, are associated with an increased risk also,2-4 and causal factors underlying this association may account for a much higher proportion of the population occurrence of the disease. Although the causes of these urban-rural differences are unknown, they have been hypothesized to include, eg, obstetric complications, infections, diet, toxic exposures, household crowding, breastfeeding, social class, and an artifact due to migration.5,6