Sixty patients with the diagnosis of reflex sympathetic dystrophy of the knee were evaluated retrospectively at our institution. The average followup was 2 years. Fifty-five (92%) patients treated with outpatient sympathetic blockade had resolution of the symptoms attributed to reflex sympathetic dystrophy. The time from onset of symptoms to initiation of treatment did not affect the ultimate outcome. The prognosis was most closely related to the presence or absence of an anatomic lesion that would continue to act as a painful stimulus. Eighty-one percent (29 of 36) of patients who had a significant anatomic lesion or surgical correction of a lesion had a complete resolution of their knee symptoms. However, only 21% (5 of 24) of patients with a persistent anatomic lesion in the knee had complete resolution. Fourteen patients required preliminary sympathetic blockade therapy before the underlying cause could be identified. This study emphasizes the need for establishing a precise diagnosis before contemplating any surgery of the knee, including arthroscopy. Arthroscopic procedures were the most common event precipitating reflex sympathetic dystrophy in this study.