Pyle disease is a rare genetic skeletal disorder which is conventionally classified with craniotubular dysplasias. The radiographic manifestations in three affected adults included widening of the metaphyseal portions of the long bones which extended through a major portion of the diaphyses, with cortical thinning and mild cranial sclerosis. The femora presented the characteristic Erlenmeyer flask configuration. Pyle disease is clinically, radiographically and genetically distinct from craniometaphyseal dysplasia, a relatively common condition with which it has been confused.