We have classified patients referred for suspicion of the Brachmann-De Lange syndrome (BDLS) into two groups using techniques of numerical taxonomy. Patients with the syndrome share an array of abnormal characteristics, and those without it have different abnormal characteristics. A group of 30 characters that best distinguish the two groups of patients was used to construct a diagnostic index. The index score is expected to divide 99% of patients into those with and without the syndrome, leaving 1% in a "zone of doubt." All 46 patients used to construct the index and 16 new patients had scores in either the BDLS or non-BDLS range and none were in the zone of doubt. A previously published index using metacarpal-phalangeal measurements, although less discriminatory, confirmed our findings in 84% of 25 patients tested, the remainder having scores in the zone of doubt for that index.