We report on genetic counseling and investigations in 36 families with inherited balanced translocations ascertained in different ways, with special regard to the completeness and reasons for incompleteness of family investigation. Quantitative evaluation of the results of cytogenetic investigations shows that non-directive genetic counseling was very effective in many families. Yet, in most of the families (34) genetic counseling and investigation remained incomplete in the sense that not all living potential translocation carriers could be counseled or investigated or that the origin of a fresh mutation could not be established by a normal karyotype in the parents of a carrier. Only in seven families could nearly all living potential carriers be counseled and investigated. The most frequent reason for incompleteness was the impossibility of transmitting or refusal to transmit information about the genetic risks to relatives (21 families), whereas direct rejection of investigation by a counseled individual was a rather rare event (18 adults). Families ascertained because of an unbalanced child seem to be more willing to transmit genetic information to relatives than families ascertained in other ways. Non-directive genetic counseling gave us an insight into the emotional problems arising during counseling of translocation families.