The bone radiographs of 43 potroom workers in an aluminium factory, on whom the diagnosis of industrial fluorosis had been confirmed by bone biopsy, are compared with radiographs from 18 control subjects. A higher frequency of ossification of ligament, tendon, and muscle attachments is observed among the fluoride exposed subjects. These changes increase with the bone fluoride content. The presence of hyperostosis is an important aid in the diagnosis of skeletal fluorosis. However, this radiological sign has to be complemented by clinical data and estimation of the concentration of urinary fluoride. Final confirmation of the diagnosis is obtained by bone biopsy.