Steatocystoma Multiplex (S.M.) is an inherited condition characterized by the appearance of cysts during the first or second decade of life. Familial cases have occasionally been reported. We studied 13 patients affected by S.M. from two unrelated families, focusing our attention on HLA, Gm and Km genotypes and on chromosomal analyses. Although we failed to correlate the syndrome with a particular HLA, Gm or Km haplotype, we report some peculiarities and differences between these two families and the healthy Italian population.