Occurrence of malignancies in the group of 267 former blood donors who donated blood 20 times and more (multiple donors) were compared with those who donated blood 10 times or less. Cohorts were comparable in age, period from the first donation and ratio of blood groups in A, B, 0 system. In the group of multiple donors, 31 (11.6%) persons were listed in the oncological register for 36 malignancies. Among the less frequent donors only 14 persons (5.3%) were listed with 15 malignancies. The difference in malignancy incidence between both groups is highly significant. The difference is significant for the cohorts of men, being not significant for women; probably because of small number of cases. Our results indicate the possibility of carcinogenic effect of the blood donation.

        Key words: blood donation, malignancy.