Polymyositis is a chronic inflammatory disease of the striated muscles that may frequently affect the lung, with the possibility of causing diffuse interstitial lung disease. Non-specific interstitial pneumonia is generally the most frequent histological findings found in this condition. In general, the recommended treatment for interstitial lung disease associated with polymyositis is prednisone together with an immunosuppressant. However, there is insufficient agreement on the initial therapeutic regime and on the best immunosuppressant. In the treatment of polymyositis, a combination of prednisone and methotrexate is recommended. However, experts in this field advise against the use of methotrexate in patients with reduced pulmonary reserve due to its potential toxicity on the lung. We present a case of non-specific interstitial pneumonia associated with polymyositis, whose pulmonary alterations were solved with prednisone. After, methotrexate was added as maintenance treatment, without observing adverse effects. Our results agree with the opinion of the authors who recommend initially treating these patients with high doses of corticosteroids in monotherapy. This option may solve the pulmonary alterations and allow us to use methotrexate as a potential candidate for the maintenance treatment. The resolution of pneumonia with corticosteroids would improve the tolerance of the patient in face of the development of a possible pulmonary toxicity induced by the immunosuppressant.