Objectives: The purpose of this study was to evaluate the accuracy of digital panoramic radiography (DP) in assessment of size reduction following the marsupialization of mandibular cystic lesions.   methodology: 10 patients those were exhibited mandibular odontogenic cystic lesions at the molar/ ramus areas were selected. These lesions were included; 7 mandibular odontogenic kerato- cystic tumors (OKCT) and 3  mandibular unicystic ameloblastoma(UAB). All lesions were exam- ined pre-marsupialization and during the follow up periods with Multi-slice CT (MSCT) Scan (that used as a gold standard) and digital panoramic radiography.   Results: There was a statistically significant difference between the (MSCT) and digital pan- orama (DP) in detecting the actual size reduction of the cystic lesions resulted from bone deposition after marsupialization. MSCT showed statistically significantly higher prevalence of validity and clearly interpretation than modality of the digital panoramic radiography. Conclusion: The digital panoramic radiography alone is insufficient tool for assessment, evalu- ation and  follow up of the  post-marsupialization  size  reduction progress of mandibular odon- togenic  cystic lesions, and  subsequently this reliance might be lead to  erroneous  professional decision related to real size reduction  of  these types of lesions.