Five members of our study family were carriers of a balanced insertion (10;5) (q22;q13;q22). One of the children had psychomotor retardation and malformations resulting from a partial trisomy of the proximal long arm of chromosome 5, having received the maternal der(10). Amniocentesis identified another case of partial proximal trisomy in a fetus of a subsequent pregnancy. This clinical and family study is compared with two other published cases of proximal trisomy 5q.