Multifocal systemic fibrosclerosis (MSF) is a multisystem disease, which often mimics malignancy. A 70-year-old asymptomatic man with lesions in the lung, prostate, submandibular glands and bile ducts appeared to have malignancy. Biopsy of a lung nodule showed IgG4-positive plasma cell infiltration and the serum IgG4 was elevated. A diagnosis of MSF was made and the patient treated with oral prednisolone at 1 mg/kg/day. Sclerosing cholangitis, retroperitoneal fibrosis, Riedel's thyroiditis, fibrotic pseudotumor of the orbit and fibrosis of the salivary glands have all been reported to be part of this disease. It is now necessary for MSF to be considered in patients with pulmonary lesions mimicking lung cancer.