Osteosarcoma of the maxilla in Hong Kong Chinese postirradiation for nasopharyngeal carcinoma. A report of four cases. Postirradiation osteosarcoma of the maxilla was seen in four Hong Kong Chinese patients treated for nasopharyngeal carcinoma. These cases represent four of 42 (9%) cases of osteosarcoma at all sites in this institution during the period 1979 to 1989, when more than 1000 patients were treated with radiotherapy for nasopharyngeal carcinoma. The latent periods varied from 8 to 11 years from completion of radiotherapy treatment to development of osteosarcoma. The radiation dosage varied from 6000 to 6280 cGy in three of the patients. These cases fit the criteria for diagnosis of postirradiation sarcomas. Maxillary osteosarcomas after irradiation for nasopharyngeal carcinoma do not appear to have been described. The very high incidence of nasopharyngeal carcinoma (for which radiotherapy is the treatment of choice) in Hong Kong Chinese would make the occurrence of such tumors more likely in Hong Kong, although the small risk does not contraindicate the use of radiation in the treatment of nasopharyngeal carcinoma in view of its well-documented efficacy. 