OBJECTIVES: The objective of this study was to review the largest single series of ectopic pregnancies treated with single-dose methotrexate reported to date. STUDY DESIGN: A review of 315 patients with unruptured ectopic pregnancies treated with single-dose methotrexate 50 mg/m2 from March 21, 1990, to March 1, 1997, was performed. RESULTS: Overall 287 patients were successfully treated with methotrexate for a success rate of 90.1%. Six patients electively withdrew and requested surgery within I week of starting therapy. Excluding withdrawals the overall success rate was 92.9%. Ten patients with an ectopic pregnancy >3.5 cm but ≤4 cm in size were treated for a 90% success rate. Forty-four patients with positive ectopic cardiac activity were treated with an 87.5% success rate. CONCLUSIONS: This large series indicates that single-dose intramuscular methotrexate for treatment of ectopic pregnancy is associated with an excellent overall success rate.