Aim: Statin therapy might be rarely associated with production of specific autoantibodies against 3-hydroxy-3-methylglutaryl coenzyme A reductase (anti-HMGCR), proximal muscle weakness, high creatine kinase (CK) levels and myofibril necrosis in muscle biopsy. Presence of these symptoms established the main criteria of a new clinical unit called Statin Induced Necrotizing Autoimmune Myopathy (SINAM). Assumed autoimmune etiopathogenesis justifies the use of combined immunosuppressive therapy. Clinical course, diagnostic criteria and therapeutic efficacy of immunosuppressive treatment are similar to that of Immune Mediated Necrotizing Myopathy (IMNM) without association with statin therapy. Methods: The group of 7 SINAM patients was classified by reassessment of the diagnostic group of 30 patients diagnosed with autoimmune myopathies based on determination of anti-HMGCR antibodies, structured quantitative revision of muscle biopsies and detailed medical history (confirming chronic statin therapy). Results: In total 30 subjects with the original diagnosis dermatomyositis, polymyositis or IMNM were tested for HMGCR antibodies. Twelve patients out of them were anti-HMGCR positive (IMNM 5x, 7x PM) and 7 of them had been on statin therapy before the symptoms developed. These 7 patients were reclassified as SINAM. Myofibrillar necrosis was found in their muscle biopsies in all cases and 5 patients also had inflammatory cell infiltration. All these patients had significantly elevated CK levels (> 10 fold) at early stage of the disease. Combined immunosuppression led to remission of clinical symptoms and normalization or significant CK level drop in all patients.