AbstractBackgroundMethotrexate‐induced pneumonitis (MTX‐P) is rare and life threatening, and a number of possible risk factors have been suggested but none are consistent between studies. Nevertheless, it can be assumed that all patients starting MTX are at risk of MTX‐P.AimThe aim of the present report is to increase awareness of the association between methotrexate and the possible risk of induced pneumonitis.Clinical detailsA 50‐year‐old man presented to a rheumatologist complaining of generalised weakness and low‐grade fever after taking 7.5 mg methotrexate (MTX) twice weekly for 1.5 months for rheumatoid arthritis. The patient was admitted to hospital due to respiratory signs and symptoms. Physical examination revealed the patient was in acute respiratory distress and mildly dehydrated. Scattered coarse crepitations were heard bilaterally and diffusely over lung fields.OutcomeA chest radiograph revealed bilateral diffuse alveolar shadowing. High‐resolution computed tomography (HRCT) showed diffuse interstitial changes, diffuse bilateral patchy alveolar shadowing and nodules. The platelet count, blood urea, electrolytes, blood sugar and liver function tests were within normal limits, while the neutrophil percentage was 90%. Owing to the symptoms, MTX‐P was suspected, the drug was discontinued and the therapy switched to oral hydrocortisone, with an observed rapid symptomatic improvement.ConclusionOur patient had a probable diagnosis of MTX‐P. Also, as per the Naranjo casualty assessment scale, he had a probable adverse drug event to MTX (score 7). The drug should be withdrawn as soon as MTX‐P is suspected and an urgent HRCT must be arranged to confirm the diagnosis. The patient should be admitted for supportive measures and corticosteroid treatment. All patients taking MTX should be educated about the symptoms of the disease and must be advised to present early to a respiratory physician. Furthermore, the patient should not be re‐treated after a definite or probable case of MTX‐P.