Dermatomyositis is a rare connective tissue disease often associated with internal malignancy and interstitial pneumonitis. Serologically, various auto-antibodies (Ab) are associated with dermatomyositis. Anti-transcription intermediary factor-1-γ/α (TIF-1-γ/α) Ab was recently identified as an auto-Ab and was observed mostly in cancer-associated dermatomyositis. IgG4-related disease is a newly described entity characterized by increased serum IgG4 levels and IgG4-positive plasma cell infiltration with fibrosis in organs such as the pancreas and parotid gland. IgG4-related disease also includes inflammatory pseudotumors in various organs. We report herein a 59-year-old Japanese man who had dermatomyositis complicated with a gastric cancer and an IgG4-related pulmonary inflammatory pseudotumor. He manifested typical classical Gottron's papules on the fingers, V-sign erythema on the chest, flagellate erythema on the back, nail fold bleeding and facial erythema. Serum levels of anti-TIF-1-γ/α Ab were positive as assessed by immunoprecipitation assay. He also had bilateral swelling of the parotid gland, and an excised specimen of the lung showed inflammatory pseudotumor with IgG4-positive plasma cells. As far as we know, this case is the first to report the association of IgG4-related disease and TIF-1-γ/α-positive dermatomyositis. Further accumulation of such cases is required to elucidate the mechanism of this association.