PURPOSE: This study describes the CT and MR findings of mucoceles occurred in the post-operative maxillary sinuses. MATERIALS AND METHODS: CT and/or MR of 19 maxillary mucoceles in 16 patients who had been operated by CaldwelI-Luc procedure were reviewed. CT scans were performed after contrast enhancement in axial and coronal planes with 5mm thickness. Three cases were studied with a 2.0 T or 0.5 T MRI, which demonstrated multi-compartment lesions. RESULTS: The lesions were bilateral in 3 cases. Compartmentalization of the antral cavity was seen in 7 out of 19 involved sinuses. Surgical bone defect of the anterior wall was the most frequent route of extension (11 cases) and extension into the infratemporal fossa with erosion of posterolateral wall was seen in 7 lesions. In 6 cases, the lesions involved orbit. The expansile and erosive bone changes were localized in every case. In one case with multi-compartment lesion, both T1- and T2-weighted MR images showed different signal intensities in each compartment which represented different protein concentration. CONCLUSION: Post-operative maxillary mucocele showed CT findings of localized erosion and bulging most frequently at the anterior wall in which the bone windows were made during the previous surgery. Post-operative compartmentalization of maxillary antrum may cause eccentric expansion of mucocete and each compartment may show different signal intensities on MR.