This retrospective study reports on sinus abnormalities detected in patients having magnetic resonance imaging (MRI) scans. Over a 12-month period, 1120 patients (aged 2-87 years) had MRI scans done for suspected intracranial pathology. Scans were reviewed independently for abnormal sinuses using four criteria: increased signal of the epithelial lining, cloudy or opacified sinus cavity, air-fluid levels, and intrasinus polyps. Thirteen percent of the 1120 patients had abnormal sinus images with the maxillary being the most involved cavity. A cloudy or opacified sinus was found in 43% of these cases. An increased signal to the epithelial lining was present in 44%. Intrasinus polyps were found in 27 paranasal sinus cavities (27 subjects). Furthermore, a seasonal pattern was evident for abnormal sinus scans. The months of July, August, September, and December had the highest frequency of abnormalities noted (greater than 16% of total scans done) whereas there was a low percentage (less than 8%) found during February and November. In summary, abnormalities of the paranasal sinuses occur frequently and vary with the time of year.