A chromosomal study was performed on 174 patients with Down’s syndrome, all inmates at an institution for the mentally retarded. Among them, 8 translocations, 1 double trisomy, 1 case of mosaicism and 1 case with a deleted extra chromosome number 21 were found. The remaining 163 cases were regular trisomies 21. Three of the translocations were of the type (14q21q), and 5 were (21qGq). The results of studies published previously in Finland, taken with the present data, give an incidence of translocations (3.2% of the total number of cases of Down’s syndrome) which agrees well with those of corresponding surveys from other countries.