We analyzed the prometaphase chromosomes of 5 patients (including one pair of sibs) with the Brachmann-de Lange syndrome (BDLS), and did not find a significant chromosome abnormality in any of them. It appears that two distinct entities can be distinguished on clinical and chromosomal bases; the BDLS and the dup(3q) syndrome. We still recommend chromosome studies in any patients with BDLS and BDLS-like manifestations.