We investigated the clinical and molecular pattern of two young men affected by dysferlinopathy, that was first diagnosed as polymyositis. We show that their symptoms and clinical course although progressive were peculiar, as well as their biopsy suggesting a subsequent analysis of dysferlin protein by western blotting. Molecular analysis of dysferlin gene revealed pathogenetic mutations in both cases. In such cases a screening with Western blot followed by DNA analysis of dysferlin gene is therefore recommended. We present a diagnostic algorythm for patients with suspected myositis but presenting signs of disease progression and poor response to steroids.