Histiocytosis X encompasses three syndromes characterized by the idiopathic proliferation of histiocytes: eosinophilic granuloma, Hand-Schuller-Christian syndrome, and Letterer-Siwe disease. At the Mayo Clinic between 1926 and 1978, 22 patients with histiocytosis X had involvement of the ear or temporal bone. These patients comprised 15% of all patients with histiocytosis X seen during that period. The ages at onset of the disease ranged from 2 months to 49 years. The most frequent otologic symptom was aural discharge (15 patients), followed in frequency by swelling in the temporal region (11 patients), vertigo (6 patients), and deafness (5 patients). Clinical findings included otitis media (13 patients), otitis externa with or without granulation tissue (10 patients), and osteolytic lesions of the temporal bone (9 patients). A high index of suspicion is required to recognize the otologic manifestations of histiocytosis X for two reasons: the systemic manifestations of the disease are often so dramatic that the ear findings are overlooked, and the otologic findings of histiocytosis X can mimic more common diseases, including simple otitis externa, aural polyps, acute mastoiditis, chronic otitis media, and metastatic lesions.