Human monozygous (Mz) twins are described with a pattern of abnormalities similar to those reported in heterozygous expression of the mouse mutant disorganisation gene (Ds). These include anomalies of the skeletal, gastrointestinal, genito-urinary and central nervous system. Concordance in Mz twins is suggestive of a genetic aetiology and lends further credence to the putative existence of a human homologue for Ds.