We report a child with clinical features remarkably similar to those of our patient reported as tetrasomy 21 in 1982. Improved banding in this, and the previous case, together with gene dosage studies, and subsequent reports in the literature lead us to conclude that these patients are in fact tetrasomic for 12p. The clinical features of these children are most distinctive and the importance of their recognition lies in the fact that the abnormal cell line is virtually confined to fibroblast studies.