A 6‐year‐old dog presented with a modified Adams stage 3 angiofibroma of the right nasal cavity, causing fluid accumulation along the right frontal sinus. Treatment consisted of step‐and‐shoot intensity‐modulated radiation therapy in 12 daily treatments of 3.5 Gy, for a total dose of 42 Gy to 95% of the planning target volume. The dog developed self‐limiting grade 2 oral mucositis which resolved within 2 weeks of course completion. A recheck exam 668 days after treatment confirmed a stable disease response by RECIST and a tumor volume decrease of 55.4%.