We report on a 12-month-old boy with pre and post-natal growth retardation, triangular face and mild psychomotor retardation. Karyotyping revealed a supernumerary marker chromosome (SMC) in 36% of cells. Using fluorescence in situ hybridization and BAC clones, the supernumerary marker chromosome was found to be a highly deleted chromosome 7 with breakpoints within the pericentric euchromatin (partial trisomy 7). Microsatellite typing indicated maternal uniparental disomy of chromosome 7 (matUPD7). The patient showed only few signs of the Silver-Russell syndrome. He therefore reflects the mild end of the phenotypic spectrum in patients with matUPD7. The case supports the argument that karyotyping is warranted in patients with short stature and only few additional features, and that UPD studies are required in patients with a SMC(7). Considering that the SMC(7) contributed very little, if any, to the phenotype of this boy, we propose that UPD7 studies should be carried out in children with pre- and postnatal growth retardation of unknown cause even in the absence of a SMC.