It is believed that the method of detection of chromosomal translocation carrier state may be a prognostic factor for the risk of giving birth to an ill child with unbalanced karyotype. For verification of this view 30 families were studied which had balanced mutual translocations identified by means of GTG banding technique in the Genetics Laboratory of the Child's Health Centre. In each family the risk was estimated of the development of an undifferentiated karyotype in live born offspring and fetuses in the 2nd trimester of pregnancy using a method evolved by Stengel--Rutkowski et al. (1988). In the group of families identified by examination of a child with abnormalities the individual risk of development of an undifferentiated karyotype in a newborn was from 0.45% to 19.78% and in a fetus it was 4.5% to 46%. In the group of families identified by spontaneous abortion the risk in the newborns was from 0 to 7% and in the fetuses in 2nd trimester it was 0 to 35%, while in the families undergoing cytogenetic examinations for indications other than reproduction disturbances the risk of an unbalanced karyotype in the newborns was from 0 to 23%, and in the fetuses from 0 to 34%. Since in each group of families high-risk translocations were found, the used methods of preliminary estimation of the risk based on the used ways of family identification are open to reservations.