Between 1982 and 1990, 81 children with localized or diffuse musculoskeletal pain, for which no cause could be found were seen in a pediatric rheumatology clinic. Forty-one children had localized idiopathic pain and 40 had diffuse idiopathic pain. Twenty-four of the patients with localized idiopathic pain fulfilled criteria for definite reflex neurovascular dystrophy. Thirty-five patients with diffuse idiopathic pain fulfilled criteria for fibromyalgia. Four patients with localized idiopathic pain (10%) developed diffuse idiopathic pain during followup; four patients with diffuse idiopathic pain (10%) had a history of localized idiopathic pain and one patient had previously been diagnosed as having Tietze's syndrome. Recurrences or persistence of pain was very common. Many children had potentially important stressors including single parent families, histories of sexual abuse, and learning difficulties. Idiopathic musculoskeletal pain is a common cause of referral to a pediatric rheumatology clinic and is often associated with significant morbidity.