In order to assess the long term effect of treatment for thyroid dysfunction on musculoskeletal symptoms, 102 patients were traced by a computer search; these patients visited two outpatient clinics of rheumatology and were known to have thyroid disorders. Of these 102 patients, 58 patients met the study criteria of having abnormal thyroid function tests at first visit to the outpatient clinic; 46 patients participated in the study. They were interviewed with a structured questionnaire about their past and current musculoskeletal complaints. The 46 patients (45 females, 1 male) had a mean age at interview of 58 years (range 21-81); 37 and 9 patients had been treated for hypothyroidism and hyperthyroidism respectively. The thyroid dysfunction was considered the only explanation of the original musculoskeletal symptoms in 24 patients (group I), in 19 patients an additional (rheumatological) diagnosis was made (group II), and in 3 patients no apparent relation between musculoskeletal complaints and thyroid dysfunction was found. After treatment for thyroid dysfunction the original complaints decreased in 52% and 47% of the patients in group I and II, respectively. At the time of the follow-up study (mean follow-up duration 67 months) 91% of the patients had musculoskeletal symptoms, 80% of the patients said their present complaints were similar to their original symptoms. Treatment for thyroid dysfunction resulted in a temporary beneficial effect on musculoskeletal symptoms in 50% of the patients; in 91% symptoms persisted.