Objective: To investigate the association of the serum levels of anti-transcriptional intermediary factor 1 (TIF1)-gamma autoantibodies with the clinical and pathological characteristics, as well as the prognosis of adult patients with dermatomyositis (DM). Methods: Eighty-seven adult DM patients with anti-TIF1-gamma autoantibodies positive screened by immunoblotting assay were enrolled in the study. The presence and levels of anti-TIF1-gamma autoantibodies were examined through enzyme-linked immunosorbent assay (ELISA). Muscle biopsy specimens were obtained from 52 patients, and immunohistochemistry was performed to visualize major histocompatibility complex (MHC)-I, CD3, CD20 and C5b-9. Muscle biopsy scores and disease activity were evaluated. Results: A total of 80 patients were positive for anti-TIF1-gamma autoantibodies confirmed by ELISA assay, including 30 cancer-associated myositis (CAM) and 50 non-CAM. Serum levels of anti-TIF1-gamma autoantibodies did not significantly differ between the CAM and non-CAM groups. The levels of anti-TIF1-gamma were associated with disease activity scores. A total of 63.9% of non-CAM patients displayed a classical DM pathological phenotype. Conversely, CAM patients presented with classical DM (25%), immune-mediated necrotizing myopathy (25%), non-specific myositis (32.3%), and normal (18%) phenotypes of muscle biopsy. Anti-TIF1-gamma autoantibody levels were positively associated with muscle biopsy total scores, muscle fiber scores and inflammatory infiltration scores in the non-CAM patients but not in the CAM patients. The survival rate of CAM patients presenting with high anti-TIF1-gamma autoantibody levels was lower than that of patients with low levels. However, no difference in survival rate was observed in the non-CAM group between high and low autoantibody levels. Conclusion: The distinct associations of anti-TIF1-gamma autoantibody levels with disease activity, muscle histopathology damage and outcome indicated that different pathogenesis might be involved in DM with or without cancer.