The aim of the current study was to analyze the frequency and characteristics of symptomatic myopathies occurring in rheumatoid arthritis (RA) patients, to correlate these findings with clinical data, and to evaluate their therapeutic implications. All RA patients from a cohort of 350 RA patients from a single institution who developed muscular symptomatology during an 8-year period were included in the study (n = 21). Clinical and laboratory data and electromyographic results were recorded in all cases, and an open muscle biopsy was performed. Weakness and muscle atrophy were the most common symptoms. Serum creatine kinase was increased in 8 cases (38%). Histopathologic study showed type 2 atrophy in 12 cases. In 13 cases, a treatable disease was diagnosed: dermatomyositis (n = 2), d-penicillamine-related dermatomyositis (n = 2), polymyositis (n = 1), muscular mononuclear cell infiltration (n = 3), polyarteritis nodosa (n = 1), glucocorticoid myopathy (n = 3), and toxic chloroquine myopathy (n = 1). In all but 1 patient, muscular clinical response to new therapy and/or drug withdrawal was satisfactory. Although symptomatic muscular involvement in RA is low (6% in the current series), we have found that nearly two thirds of cases were caused by potentially treatable conditions, mainly myositis or toxic myopathies.