Nummular eczema is a common skin disease, but the pathoetiology has yet to be elucidated. We report here a case of severe nummular eczema. Although the skin lesions were resistant to topical corticosteroids, the patient became responsive to treatment and no recurrence was noted after the eradication of dental infections. We have experienced 13 similar cases of nummular eczema with widely-distributed skin lesions. The cases had moderate to severe odontogenic infections, which were detected by panorama X-ray screening test. In 11 patients, skin lesions partially or completely improved after the dental treatment. Latent odontogenic infection may thus be an aggravating factor in treatment-resistant nummular eczema.