Human actinomycosis is a rare chronic infection caused by a bacterium of the Actinomyces genus. In the presence of a condition that will penetrate the mucosa, such as trauma or history of surgical operation, it may cross the mucosal barrier and cause infection. A 12.5-year-old girl was admitted to our clinic with complaints of pain and swelling in the right shoulder, weakness and cough. Although the patient did not have any risk factors for actinomycosis, Actinomyces was detected in the examinations. The patient was treated with penicillin. In this case report, a 12.5-year-old female patient who was diagnosed with actinomycosis with a pre-diagnosis of mass was presented.