Background: Bowen disease (BD) is a squamous cell carcinoma in situ with approximately 3-5% risk of progression to invasive carcinoma. Although surgical excision is the definitive treatment, non-surgical treatment modalities including photodynamic therapy, 5-fluorouracil, and 5% imiquimod cream could be effective alternatives for BD, especially in patients who are poor candidates for surgery. Objectives: To evaluate the efficacy and the safety of ingenol mebutate gel 0.05% in BD. Methods: A 79-year-old woman was diagnosed as BD on the calf by punch biopsy. We applied ingenol mebutate gel 0.05% on the affected area with a 0.5-cm margin, for 3 consecutive days. We observed the clinical course and the development of complications. Results: Local skin reactions including erythema, vesicles, erosion, and ulceration, as well as a moderate degree of pain at the application site peaked between day 3 and 6. The ulceration was managed with daily wet dressing and hydrophilic polyurethane foam, and it healed completely with residual postinflammatory hyperpigmentation by day 12. Ten weeks after the treatment, all the lesions were clinically resolved; multiple skin punch biopsies showed no evidence of recurrent BD. 4 months after the treatment, there has been no recurrence. Conclusion: We suggest that ingenol mebutate 0.05% gel could be a potentially effective and safe treatment option for BD.