Mucopolysaccharidosis type i (mps i) is a lysosomal storage disorder characterized by diminished degradation of the glycosaminoglycans heparan sulfate (hs) and dermatan sulfate (ds). Patients present with a variety of symptoms, including severe skeletal disease. Current therapeutic strategies have only limited effects on bone disease. The isoflavone genistein has been studied as a potential therapy for the mucopolysaccharidoses because of its putative ability to inhibit gag synthesis and subsequent accumulation. Cell, animal, and clinical studies, however, showed variable outcomes. To determine the effects of genistein on mps i-related bone disease, wild-type (wt) and mps i mice were fed a genistein-supplemented diet (corresponding to a dose of approximately 160 mg/kg/day) for 8 weeks. Hs and ds levels in bone and plasma remained unchanged after genistein supplementation, while liver hs levels were decreased in genistein-fed mps i mice as compared to untreated mps i mice. Unexpectedly, genistein-fed mice exhibited significantly decreased body length and femur length. In addition, 60% of genistein-fed mps i mice developed a scrotal hernia and/or scrotal hydrocele, manifestations, which were absent in wt or untreated mps i mice. In contrast to studies in mps iii mice, our study in mps i mice demonstraes no beneficial but even potential adverse effects of genistein supplementation. Our results urge for a cautious approach on the use of genistein, at least in patients with mps i.