In a large kindred with multiple endocrine neoplasia type 2a (MEN 2a) (137 members, 5 generations), bilateral thyroid medullary carcinoma was found in all affected members. Pheochromocytoma was present in 59% of the cases, and was responsible at least for 4 out the 5 deaths related to MEN 2a. Hyperparathyroidism was less frequent (41%). Family screening leads to a reduction in age for diagnosis and to an improvement in the prevalence of complete healing after surgery. Linkage between HLA loci and a dominant gene for MEN 2a was investigated in this kindred. Lod scores for recombination fraction were all negative (-0.47 for a recombination fraction of 0.05). These results comfort the lack of linkage between MEN 2a and the HLA complex.