Many persons with schizophrenia have severe cognitive impairments. Few studies have investigated the relationship between risk factors for schizophrenia and cognitive functioning. This study examined cognitive functioning in schizophrenia and schizoaffective disorder and how cognitive functioning is related to clinical characteristics and schizophrenia risk factors, namely low and high birth weight, male sex and originating from a Finnish internal isolate with high schizophrenia risk.The results suggested that symptom severity may predict the level of cognitive dysfunction better than the categorical diagnosis of schizophrenia or schizoaffective disorder. The schizophrenia risk factors had distinct associations with cognitive functioning. Both low and high birth weight were associated with small cognitive impairment. In schizophrenia families, persons originating from the internal isolate had better cognitive performance than those originating from the rest of Finland. Sex did not affect the level of cognitive impairment in persons with schizophrenia or in their first-degree relatives.