Now that we know about the genetic production mechanisms of diseases of the trophoblast, interest is concentrated on the question which risk factors can produce a disposition in the patient - seen from a clinico-genetic angle - towards malignancy of a complete mole. Many years before the genetic interrelations became known, there had been discussions on blood relationship as a possible aetiological factor in the production of chorionic carcinoma. Since consanguinity in preceding generations can lead to a selection of certain genotypes, this question was reexamined on a limited patients material (10 patients with chorionic carcinoma and 11 with mole). The negative result of this study contradicts - similar to other recent publications on this subject - the hitherto frequently advanced hypothesis that homozygotism is responsible, for a recessive "onko" gen, for rendering a complete mole malignant. Recent investigations, for example, point to a close correlation between the presence of a Y chromosome in a complete mole, and malignancy.