Treatment of a maxillary second premolar with an associated cystic lesion through conventional endodontic therapy combined with decompression and cyst enucleation is reported. Although cystic lesions frequently heal simply with endodontic therapy, refractory large lesions after nonsurgical endodontic treatment may require additional diagnosis and treatment. In this case, conventional root canal treatment resulted in incomplete healing and required further surgery. Following cyst enucleation with biopsy of the lesion and apical surgery on the tooth, the cause of the refractory lesion was found to be associated with foreign latex material in the periapical tissue, which was speculated to have originated from exposure to a dental glove. At the 1-year follow-up visit, the lesion exhibited continued resolution. Schlagwörter: cyst, endodontic, foreign body, latex, periapical