The G-banded chromosomes of peripheral blood from 55 patients with clinically and/or pathologically diagnosed trophoblastic tumors, husbands of 45 patients with the disease and 181 female and male normal controls were analyzed. Loss of chromosome 22, sporadic translocation of chromosome 7; 14 and low percentage mosaicism of sex chromosomes were noted. Significantly increased frequencies of the latter two abnormalities as well as another one, pericentric inversion of chromosome 9, were detected in both the patient and the husband groups, suggesting that these chromosome abnormalities might be causal factors of trophoblastic tumors.