OBJECTIVES: To describe secondary acquired cholesteatoma in patients previously treated for Langerhans cell histiocytosis (LCH). To focus on misleading symptoms suggesting LCH relapse. PATIENTS: This study involved 3 patients aged 12, 20, and 58 months whose conditions were diagnosed with LCH. All 3 had involvement of the mastoid and of the skin of the external ear canal (EAC) at diagnosis. They were treated with steroids and vinblastine. INTERVENTIONS: Serial computed tomographic (CT) scans and clinical follow-up. MAIN OUTCOME MEASURE: Exploratory surgery of the mastoid. RESULTS: Otorrhea recurred in all 3 patients at 24, 17, and 26 months, respectively, with difficulties to clinically identify a hole in the posterior part of the EAC. The otorrhea was considered a sign of a new occurrence of LCH, leading to systemic chemotherapy in 2 cases. A CT scan showed a defect in the posterior wall of the EAC and suggested cholesteatomatous invasion of the mastoid (2 true cholesteatomas and 1 precholesteatomatous case).Surgery (canal wall up mastoidectomies) successfully removed the cholesteatoma (bilateral in 2 cases) and reconstructed the bony defect using cartilage. Biopsies ruled out LCH recurrence. CONCLUSION: Secondary acquired cholesteatoma (through a bony defect of the EAC) may occur in patients previously treated for LCH. Recurrence of symptoms and bone destruction on CT may wrongly suggest LCH recurrence. Surgery allows removal of the cholesteatoma as well as EAC reconstruction and control biopsy.