This paper summarizes the worldwide cumulative experience with copolymer 1 (Copaxone) in 857 patients who were enrolled in open-label (n = 586), double-blind (n = 201), and compassioniate-use studies (n = 70). The results of a phase III study, including previously unpublished information, are employed to delineate adverse events that occur more frequently among patients treated with copolymer 1 than in placebo-treated controls, and to provide qualitative information. In the cumulative database, patients usually had relapsing-remitting multiple sclerosis and typically received a dose of 20 mg by daily subcutaneous injection for at least 1 year, and occasionally for more than 10 years. Withdrawal rates were 8% for copolymer 1 and 2% for placebo. The most common adverse event was mild injection-site reaction, manifested by erythema, inflammation, and induration. The most remarkable adverse event was a systemic post-injection reaction that occurred in 10% of patients. It was manifested by flushing, chest tightness, palpitations, dyspnea, and anxiety, and was acute and transient. The incidence of adverse events associated with interferon beta, such as flu-like syndrome, depression, hematologic abnormalities, cardiotoxicity, and elevated hepatic enzymes, was not increased among patients treated with copolymer 1. Evaluation of the extensive experience with copolymer 1 confirms that it is well tolerated and suitable for self-administration by patients with multiple sclerosis.