It is well established that cognitive deficits are an almost invariable component of the schizophrenia syndrome. Much less is known about the association of cognitive deficits and the range of psychiatric disorders. The current study made use of a Swedish conscript cohort which included an IQ assessment and full psychiatric evaluation at conscription of all 18- to 19-year-old males. It was found that reduced intellectual functioning was found in association with psychosis and neurotic disorders including depression, personality disorders, alcoholism, and drug dependence. The effect was particularly strong for alcoholism. This presumably represents a combination of premorbid deficits (as demonstrated in those who developed schizophrenia some years later) plus coincident impairments. The direction of causality of this latter association is likely to be both forward and reverse. Different cognitive subtests showed varied strengths of association: "mechanical ability/knowledge," which might reflect planning and reasoning more than the other subtests, had the strongest effect. Cognitive deficits are widespread in psychiatric disorders and should be taken into account in clinical interactions.