Chondroblastomas are unusual benign lesions of bone. They classically occur at the ends of long bones in young persons. The roentgenographic and histologic features are typical. We had an opportunity to study a large number of chondroblastomas. Most of the cases came from the consultation file started by Dr D. C. Dahlin at the Mayo Clinic. This method of ascertainment may tend to load our series with unusual and atypical examples. We found some unusual locations, such as the skull and facial bones and the small tubular bones of the hands and feet. We also found some unusual histologic features, such as mitotic activity, necrosis, and cellular atypia. However, despite the unusual features, the biological behavior of these tumors was that of a benign process with only limited local aggressiveness.