Toxoplasmosis, a worldwide zoonosis caused by a coccidian parasite Toxoplasma gondii, is more often asymptomatic in immunocompetent patients. We report the case of a 38-year-old immunocompetent male with a polymyositis as the presenting manifestation of T. gondii infection. The patient was hospitalized for a 30-day history of fever (T max 39.5°C), muscle pain, and progressive weakness of the muscles. A diagnosis of polymyositis was made, and he was started on corticosteroid treatment, which caused no reduction of symptoms. After finding a positive polymerase chain reaction (PCR) assay for T. gondii, together with additional clinical findings, a diagnosis of acute toxoplasmosis was made. Specific treatment with pyrimethamine and sulfadiazine was started, with a progressive reduction of symptoms and normalization of laboratory tests.