Neurofibromatosis 1 is an autosomal dominant disorder. Noonan's syndrome is known to be associated with neurofibromatoses. Patients with neurofibromatosis are predisposed to developing malignant tumors. The relationship between the genetic changes in the neurofibromin gene and mechanisms associated with tumor development in neurofibromatosis has been investigated. A nonsense mutation C2446T-->R816X of the neurofibromin gene has been detected in some patients with the neurofibromatosis 1-Noonan's syndrome phenotype. We describe a case of an infant with the overlapping features of neurofibromatosis I and Noonan's syndrome who presented with rhabdomyosarcoma of the urinary bladder. The genetic analysis of our patient revealed neither mutation in the neurofibromatosis 1-guanosine triphosphatase-activating protein-related domain nor the R816X nonsense mutation. The phenotypic and genotypic features of neurofibromatosis, Noonan's syndrome, and cases with the overlapping features of both syndromes have been reviewed. The presentation of our case underlines the importance of careful examination for the clinical features of neurofibromatosis and phenotypic traits of associated diseases, especially in patients with malignant tumors.