Objective: To investigate bone formation after enucleation of mandibular odontogenic keratocysts (keratocystic odontogenic tumours) by computed densitometry of preoperative and post-operative panoramic radiographs. Methods: Fifty-eight patients with mandibular keratocysts were treated by surgical enucleation and primarily closed without grafting. The largest diameters of the cysts were 3.5 cm to 7.1 cm. Post-operative clinical and radiographic examinations were performed at 1, 3, 6 and 12 months. Bone density of the residual cavity was measured on the preoperative and postoperative panoramic radiographs with Digora® through a greyscale of 254 tonalities. Student t test was used for comparison of bone density values of different time periods. Results: Progressive bone formation in the residual cavity was observed after enucleation of mandibular odontogenic keratocysts. The mean increase of bone density was 6.85% at post-operative 1 month, 22.61% at 3 months, 49.45% at 6 months and 71.77% at 12 months in comparison with that of the preoperative radiograph. Although increase in bone density was not significantly different between the post-operative first 3 months and second 3 months, this increase was significantly higher in the first 6 months than that in the later 6 months (P 0.05). No significant correlation was found between increase of bone density and patient gender or the maximal diameter of the cysts. Conclusion: Bone regeneration could progressively occur in the defect area without grafting materials after enucleation of mandibular odontogenic keratocysts, with significant increase of bone density at 6 months post-operatively. Keywords: bone healing, computerised analysis, enucleation, odontogenic keratocyst, panoramic radiographs