OBJECTIVES--To examine the intended meaning of words used by patients to describe arthritic symptoms, and to distinguish between different patient groups on the basis of these words. METHODS--A Joint Symptom Questionnaire, developed to resemble the McGill Pain Questionnaire, was given to health professionals (n = 50) and patients with rheumatoid arthritis (RA) (n = 100), fibromyalgia (FM) (n = 50), ankylosing spondylitis (AS) (n = 50), and osteoarthritis (OA) (n = 50). Respondents were invited to define each word by selecting an appropriate heading. Comparison of patient groups was based on the selection of words they chose to describe their joint symptoms. RESULTS--Between health professionals and patients there were no semantic differences in the words given. Patients with FM chose more words to describe their symptoms than the other patient groups (RA median nine words; AS nine words; OA 10 words; FM 12 words). Using receiver operating characteristic curves, a clear distinction between patients with RA, FM, and AS was found, but patients with RA were not readily separated from patients with OA. CONCLUSIONS--There appears to be no semeiological confusion between health professionals and patients regarding arthritic symptoms. However, the spectrum of words chosen by patients to describe the feelings in their joints permits a separation between patients with RA, AS, and FM. Using this questionnaire, patients with RA and OA are symptomatically similar.