To analyze the clinical characteristics and outcome of Langerhans' cell histiocytosis that developed in patients younger than 2 years and to compare them with those of older patients.

The chief complaint, age of onset, site and number of bone involvements, systemic organ involvement, treatment and final outcome of fourteen cases of histologically proven Langerhans' cell histiocytosis that developed in patients younger than 2 years were analyzed retrospectively and compared with the results from those of fourteen older patients. The Fisher Exact test was used for statistical analysis.

Langerhans' cell histiocytosis that developed in patients younger than 2 years had a more advanced stage (2.5/1.1), multiple bone involvement (2.7/1.7 sites) and a higher rate of systemic organ involvement (29%/0%). It required chemotherapy more often (9/2 patients). There was also a trend of frequent relapse and a lower rate of complete healing, but this was not statistically significant. Among the 62 bone lesions, 47 were healed by simple observation or systemic chemotherapy without the need for surgical intervention.

Langerhans' cell histiocytosis that developed in patients younger than 2 years showed multiple bone involvement, more systemic involvement and a high recurrence rate. It also required systemic chemotherapy more often. However most bone lesions were managed successfully without the need for surgical intervention.