Background: Sino-nasal aspergillosis is a common nasal disease in dogs. Recommended treatment protocols typically involve trephination of the frontal sinuses or the use of an antifungal solution instilled into the frontal sinus under anesthesia, both of which have associated morbidity and complications. Objectives: To assess a minimally-invasive topical treatment protocol for sino-nasal aspergillosis in dogs. Animals: Twelve client-owned dogs diagnosed with sino-nasal aspergillosis that completed recommended treatment. Methods: Medical records were retrospectively reviewed to identify dogs with sino-nasal aspergillosis that received treatment. Fungal plaques were manually debrided and irrigated via frontal sinuscopy in 12 dogs that then were treated topically with 1% topical clotrimazole cream. Irrigation and topical medication application was achieved using a catheter placed retrograde directly into the frontal sinuses using the Seldinger technique over a guidewire, thereby avoiding the need for frontal sinus trephination. Invasion into the calvarium was recorded before treatment but was not considered a criterion for exclusion. Debridement and cream deposition was repeated every 2 weeks as needed until negative culture and histopathologic findings were obtained. Results: All dogs were cured (negative results for Aspergillus on endoscopy, fungal culture, and histopathology) with a median of 2 treatments. Treatments were well tolerated, with minimal adverse effects reported. Three dogs had evidence of erosion into the calvarium on computed tomography imaging. Conclusions and Clinical Importance: This protocol appears to be an effective and well-tolerated minimally invasive treatment for sino-nasal aspergillosis, including in dogs with erosion into the calvarium. Only mild adverse effects were noted.