To determine the efficacy and safety of primary medical treatment with systemic methotrexate (MTX) in caesarean scar ectopic pregnancy, we conducted a Medline/PubMed search on the relevant English literature from January 1978 to January 2012. The search yielded 27 publications of 40 cases of caesarean scar ectopic pregnancy. The literature search showed a very liberal use of systemic MTX treatment with unfavourable outcomes, although the major determinant of the clinical efficacy was found in here to be beta-hCG level together with embryonic cardiac activity (ECA) status. A caesarean scar ectopic pregnancy presented with a serum beta-hCG concentration of <= 12,000 mIU/ml (odds ratio, OR 5.68, 95% confidence interval, CI, 1.37-23.48) and absence of ECA (OR 4.80, 95% CI, 1.14-20.08) was found to be associated with higher efficacy rate of primary systemic MTX treatment. Administration of primary systemic MTX treatment was found to be ideal for a caesarean scar ectopic pregnancy presented before 8 weeks' gestation, with a beta-hCG concentration of <= 12,000 mIU/ml together with an absent ECA (OR 14.52, 95% CI, 2.36-89.09).