Even before schizophrenia is apparent, people who will later develop it have generally worse school performance and lower IQs than their peers. Tiihonen et al. (p. 1904) examined the nature of the impairment and whether it also occurs in bipolar disorder and other psychoses. Results of tests measuring verbal, arithmetic, and visuospatial reasoning were available for 195,019 men conscripted into the Finnish military between 1982 and 1987. The Finnish Hospital Discharge Register was used to identify conscripts later hospitalized for psychosis. By 1992, 100 of the men had been hospitalized with bipolar disorder, 621 with schizophrenia, and 527 with other psychoses. The earlier test results showed that all three diagnostic groups had impaired visuospatial reasoning before identification of the illness. A dose-response relationship was evident—the lower the score, the greater the risk of illness. Surprisingly, men who developed bipolar disorder had higher arithmetic scores, perhaps because of exaggerated alertness and psychomotor activity.