A 36-year-old female patient sought out a periodontist, complaining of painful oral lesions with a 9-month evolution. According to her, the gum "came to pieces". She presented areas of erythema in the marginal gingiva, which were more visible in the lower anterior teeth region. Lesions were associated with edema and erosion, followed by ulceration. The condition was initially misdiagnosed and treated as inflammatory periodontal disease. After, the patient searched for a stomatologist who found, in addition to desquamative gingivitis, ulcerated areas on the dorsum and lateral edges of the tongue. The clinical suspicion of pemphigus vulgaris or pemphigoid of the mucous membranes was raised. Topical corticosteroid therapy was employed, with reduction of the pain. An incisional biopsy confirmed the suspicion of pemphigus vulgaris. Systemic corticosteroid therapy was also introduced, resulting in a considerable reduction of the lesions. The patient had some side effects of corticosteroid therapy, and is undergoing follow-up. A 36-year-old female patient sought out a periodontist, complaining of painful oral lesions with a 9-month evolution. According to her, the gum "came to pieces". She presented areas of erythema in the marginal gingiva, which were more visible in the lower anterior teeth region. Lesions were associated with edema and erosion, followed by ulceration. The condition was initially misdiagnosed and treated as inflammatory periodontal disease. After, the patient searched for a stomatologist who found, in addition to desquamative gingivitis, ulcerated areas on the dorsum and lateral edges of the tongue. The clinical suspicion of pemphigus vulgaris or pemphigoid of the mucous membranes was raised. Topical corticosteroid therapy was employed, with reduction of the pain. An incisional biopsy confirmed the suspicion of pemphigus vulgaris. Systemic corticosteroid therapy was also introduced, resulting in a considerable reduction of the lesions. The patient had some side effects of corticosteroid therapy, and is undergoing follow-up.