The radiological interpretation of postoperative changes of the paranasal sinuses requires knowledge of why and how the surgical intervention was performed and what the basic clinical findings were. It is important to know whether there was an inflammation, a reconstructive procedure, or a tumorous process. Multidetector computed tomography (MDCT) evaluated in a high-resolution bone window level setting represents the method of choice for imaging after nonfunctional and functional procedures after inflammatory changes as well as for imaging after reconstructive surgery because of facial trauma or before dental implantation. In the postoperative follow-up of tumor patients contrast-enhanced MDCT evaluated in a soft tissue window and bone window and especially magnetic resonance imaging (MRI) represent the standard. In many cases it is possible to differentiate tumor recurrence from inflammation with the help of contrast-enhanced multiplanar MRI and to detect bone marrow changes prior to CT.