An infant with non-mosaic 9p tetrasomy is described. The tetrasomy apparently results from a translocation involving the 9qh region. All the cells analyzed from multiple banding techniques from lymphocyte culture as well as skin fibroblast culture were 9p tetrasomic. The infant, who had the characteristic dysmorphic features of 9p tetrasomy, survived for 2 months. Prominent features included: low birth weight, severe retardation, brachycephaly with large anterior fontanelle, hypertelorism with short bilateral palpebral fissures, beaked nose, bilateral cleft lip and palate, and low-set, malformed ears. Skeletal anomalies, ambiguous genitalia and heart defect were also observed. These features are highly characteristic of the 9p tetrasomy syndrome based on six pure tetrasomy and four cases of tetrasomy that included part of the 9qh region.