A 4 yr old boy with partial trisomy 11q resulting from malsegregation of a maternal translocation, t(11;22)(q23;1;q11.1), exhibitis severe mental deficiency, growth retardation and hypotonia, brachycephaly with flattened occiput and forehead, facial dysmorphia and pre-auricular fistula. These features are in agreement with the syndrome recently described for partial trisomy 11q. The translocation appears to be identifical to that in 3 other families already reported.