The keratocystic odontogenic tumour (KCOT) is a relatively common oral and maxillofacial lesion that derives from remnants of the dental lamina. It is aggressive, grows rapidly and invades the surrounding tissues. Various treatment modalities and differing recurrence rates have been reported for KCOT. After an initial diagnoses of KCOT marsupialisation with posterior enucleation was assign as a possible treatment to a 36 year old female. Ten months after marsupialisation patient had a new CT scan were was possible to observ that the defect was filled completely with newly formed bone tissue. Patient was follow for 2 years. This case shows that a large KCOT can be treated with a combination of conservative and aggressive methods and that conservative methods can play an important role in the final outcome.