BACKGROUND Ectopic pregnancy (EP) is a condition presenting as a major health problem for women of childbearing age. This study aimed to identify potential risk factors for EP and to evaluate the contribution of the risk factors associated to EP. METHODS This retrospective nested case-control study was conducted from 2006 to 2011. In case group, there were a total of 83 women diagnosed with EP, while in the control group; there was a total of 340 women who gave birth. The basic recorded information included surgical, gynecological, obstetrics, sexual, contraceptive, and infectious histories; demographic characteristics; smoking habits; fertility markers; as well as reproductive outcome after EP. The association between EP and the factors studied was analyzed by logistic regression. RESULTS The findings reveal that the following factors were associated with increased risk of EP, including: Maternal age (odds ratio [OR] =1.11, confidence interval [CI] [1.06-1.16], P < 0.0001), spouse's cigarette smoking (OR = 1.73, CI [1.05-2.85], P = 0.02), gravidity (OR = 1.50, CI [1.25-1.80], P < 0.0001), prior spontaneous abortions (OR = 1.93, CI [1.11-3.36], P = 0.01), history of EP (OR = 17.16, CI [1.89-155.67], P = 0.01), tubal blockage (OR = 10.85, CI [2.02-58.08], P = 0.01), use of intrauterine device (IUD) (OR = 4.39, CI [1.78-10.81], P = 0.001), tubal damage (OR = 2.704, CI [1.26-5.78], P = 0.01), first pregnancy interval (OR = 1.01, CI [1.00-1.02], P < 0.0001) and history of infertility (OR = 6.13, CI [2.70-13.93], P < 0.0001). CONCLUSIONS By identifying risk factors being amenable to modification, such as cigarette smoking and use of IUD and first pregnancy interval the effective risk-reduction strategies can be devised.