A four year old girl with severe mental retardation and multiple congenital abnormalities manifested "partial trisomy 15". Her mother, pregnant at the time of examination, possessed a balanced translocation which, after banding techniques, was identified as t(4;15)(p16;q22). Amnio-centesis revealed the karyotype of the fetus to be identical to that of the proposita and a therapeutic abortion was performed. Prenatal investigation of a subsequent pregnancy revealed a normal male karyotype. Comparison of the proposita and aborted fetus of this family with the 5 reported other cases of "partial trisomy 15" does not allow for a precise recognizable clinical syndrome.