Postirradiation pseudosclerodermatous panniculitis is a rare complication of radiation therapy that presents as an indurated plaque and/or subcutaneous nodule in an area of previously irradiated tissue. The histopathologic pattern is of mixed lobular and septal panniculitis with necrotic adipocytes and thickened sclerotic septa as well as dense inflammatory infiltrates consisting mainly of histiocytes. The typical time interval is 1 month to several years after treatment with radiation therapy. This is a case of an 86-year-old man with a medical history significant for diffuse large B-cell lymphoma who was given 3 fractions of stereotactic body radiation therapy for treatment of stage IA non-small cell lung adenocarcinoma of the right upper lobe. Two years later, he presented with several small palpable subcutaneous right axillary nodules, which coalesced into a 6-cm firm multilobulated right axillary mass over several weeks. Histopathology showed sclerosing panniculitis with lipomembranous changes and septal fibrosis. This is the first reported case describing postirradiation pseudosclerodermatous panniculitis in a patient with lung cancer treated with stereotactic body radiation therapy. This diagnosis must be differentiated from other subtypes of panniculitis and complications of radiation therapy.