Fifteen children with autosomal reciprocal translocations were found in an incidence study of chromosome aberrations among 11,148 consecutively liveborn children in a Danish Maternity Hospital (1.34 per 1,000). The segregation rate of the balanced forms was 60% and that of unbalanced forms 4%; the frequency of familial cases was 73%. None of the probands or their relatives who carried the balanced translocation had any physical or mental abnormalities which could be associated with the chromosome aberration. We found two children with unbalanced translocations among the 45 relatives examined, but more studies of unselected population groups are needed before any segregation rates for unbalanced derivatives of autosomal reciprocal translocations can be estimated. We found a significantly higher frequency of abortions, stillbirths and perinatal deaths in the progeny of carriers with the translocation, compared with non-carriers in the same families. The unbalanced forms of autosomal reciprocal translocations in most cases are probably not compatible with the development of a foetus to a liveborn, healthy child. Fifteen children with 13/14 translocation were found among 11,148 consecutively liveborn children. Incidence, segregation rates and type of translocation are discussed. Fertility and risk for carriers of D/D translocations of producing children with autosomal trisomy are discussed.