Oral mucosal involvement of autoimmune progesterone dermatitis is exceedingly rare. This report presents a woman with very painful ulcerative stomatitis that recurred with every menstrual period, in the absence of other clinical manifestations. Ulcers were eventually controlled with oral tamoxifen treatment for three months. Subsequent follow-up visits showed complete resolution of her oral ulcerative lesions. The non-specific nature of her oral ulcers resulted in multiple medical and dental consultations and a delay in reaching the final diagnosis. Clinicians should be aware of the possibility of progesterone hypersensitivity when painful oral ulcerative lesions appear concurrently with each progesterone surge.