Aim: This study was designed to evaluate the shrinkage pattern of odontogenic cyst after surgical decompression clinically and radiographically. Subjects and Methods: Twenty-eight patients were selected from those attending the outpatient clinic of the Department of Oral and Maxillofacial Surgery, Sayed Galal University Hospital with cystic lesions, larger than 3 cm on 2D-Panorama. Clinical examination was made to all patients as: Facial disfigurement, Intra-oral swelling and Sinus tract. Preoperative and after 3, 6 months postoperatively cone beam CT for every patient to determine extension of the cystic lesion, Proximity to the vital structures, Multi or uni-cystic lesion and Volumetric measurement of cystic lesion. All readings were recorded and analyzed statistically. Results: The mean volumetric analysis was 21.21 ± 7.69 cm3 at base line (pre surgery), 13.96 ±5.25 cm3 after 3 months and 8.80± 4.03 cm3 after 6 months which was statistically significant. Conclusion: Decompression is an effective treatment of odontogenic cysts, leading to a high percent reduction of the lesion area