A ring chromosome 2 mosaic [46,XX/46,XX,r(2)(p25q37)] was found in a newborn female with severe intrauterine growth retardation (IUGR), postnatal growth failure, and a few minor abnormalities. Psychomotor development has been normal to 19 months old. A ring chromosome 2 is present in 77.8% of the nuclei examined and is not found in the parents or a sibling. G- and R-banding reveal the break points to be p25q37. The presence of a normal cell line indicates that the chromosome abnormality arose after conception.