Rhinolith caused by actinomycosis is rare; to the best of our knowledge, only two cases have been reported in Japanese and English medical literature. A 19-year-old woman had been suffering from a left nasal obstruction for several years. A large brown mass was found in the left nasal cavity. Actinomycosis was suspected based on a histopathological examination of a biopsy specimen. Computed tomography showed a calcified lesion in the left nasal cavity and mucosal hypertrophy in the left maxillary sinus. Based on these findings, the mass lesion was diagnosed as a rhinolith associated with actinomycosis that had caused left maxillary sinusitis by obstructing the ostium. The lesion, which weighed 3.8 grams, was removed via an endscopic endonasal approach. Histopathological examination revealed an actinomycotic body. Chemical analysis revealed a composition of phosphates, protein, and carbonate. Postoperatively, the patient was treated with clarithromycin for 3 months, and the left maxillary sinusitis improved.
