A 7-week-old full-term girl was referred to our clinic for persistent and expanding diaper dermatitis present since 1 week of age. She was initially treated at an outside hospital with intravenous clindamycin hydrochloride for presumed perianal cellulitis and was discharged with a regimen of oral clindamycin hydrochloride. When the patient was aged 4 weeks, the lesion became ulcerated and she was admitted to our hospital. She was given intravenous antibiotics and mupirocin, 2%, ointment, triamcinolone, 0.1%, ointment, clotrimazole, 1%, cream, nystatin cream, and zinc oxide paste. Results of cultures for bacteria and herpes simplex virus were negative. The patient had no systemic symptoms and was discharged and scheduled for an outpatient dermatology appointment.