AbstractWhile bony exostoses of the external auditory canal have long been recognized as a complication of cold‐water swimming, bony exostoses of the paranasal sinuses have not been previously reported. We present an unusual case of multiple exostoses of the paranasal sinuses, which began coincident with nasal irrigation with cold gentamicin solution. The patient had had prior endoscopic sinus surgery. Topical antibiotic gentamicin irrigation lessened recurrence of bacterial sinus episodes. He admitted to using the irrigation directly from the refrigerator daily for two years. A biopsy was consistent with exostosis. Patients should be counseled to avoid irrigating their paranasal sinuses with cold irrigants. Laryngoscope, 2010