A severely mental and motor retarded hoe with monosomy 9pter -> p22, trisomy 10q26 -> qter due to paternal reciprocal translocation 46,xy,t(9;10)(p23;q26): We report on a twenty-two months old male patient with hypotonia, mental and motor retardation and trigonocephaly. Standard GTG banding chromosomal analysis (from metaphyses of a periferal blood lymphocyte culture) showed 46,XY, der(9) monosomy 9pter -> p22, trisomy 10q26 -> qter karyotype. This unbalanced translocation resulted from the father's (9,10) (p22;p26) karyotype. Deletions of the terminal part of 9p and partial trisomy of chromosome 10q are rare chromosomal disorders. To our knowledge, this is the first case report in the literature of a deletion of 9pter -> p22.3 and a duplication of 10q26 -> qter. We assume that the clinical anomalies are due to der(9) monosomy 9pter -> p22, trisomy 10q-26qter.