We report on 3 Puerto Rican brothers with the clinical and laboratory findings of aspartylglucosaminuria (AGU). Their parents were first cousins. The affected sibs have the "cardinal" manifestations of AGU, including developmental disabilities, progressive "coarsening" of the face, and early onset of hepatosplenomegaly. Biochemical studies showed elevated levels of urinary aspartylglucosamine and very low activity of aspartylglucosaminidase(AGA) in cultured fibroblasts. With long term follow-up, previously undescribed manifestations were noted, including radiographic evidence of spondylolysis and spondylolisthesis in early childhood and development of macro-orchidism during puberty. This family shows that AGU is not limited to individuals of Finnish background, but that the gene is panethnic in distribution and that additional changes, not previously noted, may present with advancing age.