Fibrous dysplasia involving the sphenoid sinus and the entire left sphenoid bone, manifested clinically by left proptosis and frontal headaches, was disagnosed in a 13‐year‐old black male. The case is unusual since it is only the third reported instance of fibrous dysplasia of the sphenoid sinus, and because the disease became clinically apparent at the onset of puberty in the patient. Since previous reporters have suggested that fibrous dysplasia remains stable or progresses slightly after the onset of puberty, the patient was not treated with radical surgery, but instead was observed closely. At this point, one year following admission, the patient's proptosis has disappeared and his symptoms are markedly improved.