Background. Keratinizing odontogenic cysts of the mandible commonly have an aggressive clinical course, marked by multiple recurrences. Primary intraosseus carcinoma (PIOC) of the mandible is rare, and when it occurs it is often found to be arising in or closely associated with some type of cystic structure.

Methods. A patient with squamous cell carcinoma arising from an odontogenic keratocyst is studied clinically, radiographically, and pathologically.

Results. The patient who was documented to have an odontogenic keratocyst, 1 year later had a squamous carcinoma removed from the recurrent cyst.

Conclusion. We report the occurrence of squamous cell carcinoma arising from a recurrent odontogenic keratocyst, which has not previously been documented in the literature. The literature on this subject is reviewed. © 1994 John Wiley & Sons, Inc.