Langerhans cell histiocytosis (LCH) is a proliferative disorder of Langerhans cells and extremely rare in adults. Adult LCH is often associated with osteolytic bone lesions, but large bone-defective lesions have been rarely reported. We report an adult case of LCH accompanied by large osteolytic lesions in the skull that successfully responded to chemotherapy. A 47-year-old woman with LCH who had multiple, large osteolytic areas of more than 3 cm in diameter in the skull was admitted to our hospital. She was treated with systemic chemotherapy consisting of prednisolone, vinblastine, and 6-mercaptopurine. Twelve months later, when she completed the treatment, osteolytic areas were covered with hard osseous tissue, and X-ray examination confirmed regeneration of the bone. This case indicates that chemotherapy can be effective even for the treatment of large osteolytic lesions in adult LCH patients.