Twenty-five families including 34 individuals with common variable immune deficiency (CVID), with at least one affected female in each family, were studied. The distribution of cases within families was compatible with autosomal recessive inheritance, making it plausible to test hypotheses about the disease risk of heterozygote carriers of putative CVID genes by comparing the frequency of autoimmune disorders and cancer in 1033 adult blood relatives to that in 566 spouse controls. For cancer, observed numbers of cases or deaths were also compared to expected numbers derived from population rates. No single family had an unusual clustering of autoimmune conditions, and, overall, autoimmune disease was not found more frequently in blood relatives than in spouse controls. Blood relatives did have a modest, although not significant, excess of rheumatic heart disease. For cancer analyses, comparisons with general population rates indicated no heterozygote predisposition, while direct comparisons of blood relatives to spouse controls revealed a significantly elevated cancer rate in females (rate ratio = 2.3, P less than 0.003). The estimated relative risk of cancer for female CVID heterozygotes was most elevated in the 45-69-year-old age group. It is arguable whether comparisons with population or spouse controls are the most appropriate for evaluating the cancer risk of CVID heterozygotes. The hypothesis that the CVID gene predisposes heterozygous female carriers to cancer may be evaluated more easily in the future when the genetic basis for CVID is better understood.