We describe a case of dermatomyositis with concurrent clinical and laboratory features of idiopathic thrombocytopenia associated with anti-Ku antibody. A diagnosis of dermatomyositis was established by the characteristic skin changes together with a muscle biopsy. Scintigraphic studies indicated cardiac involvement. Autoimmune idiopathic thrombocytopenia (AITP) has been described in association with both systemic lupus erythematosus (SLE) and scleroderma, but there are few reports describing AITP associated with myositis. To our knowledge, this is the first report of a case of dermatomyositis associated with AITP and anti-Ku antibody.