Clinical and cytogenetic studies of a six-year-old boy with multiple anomalies, including growth retardation, mild mental retardation, diffusely scattered minute areas of skin hypopigmentation, and skeletal abnormalities, are presented. Chromosomal analysis of lymphocytes, skin fibroblasts, and marrow cells showed a significant proportion of cells to have a tetraploid number of chromosomes. An extra 18 chromosome was present in approximately 10% of the cells from peripheral blood.