Objective To detect if removing the cervical mucus before performing intrauterine insemination (IUI) could improve pregnancy outcomes in patients with unexplained infertility.Design Prospective randomized study.Setting An Egyptian University Hospital.Population Seven hundred and fourteen couples with unexplained infertility who underwent intrauterine insemination (IUI) with or without cervical mucus removal.Methods Using computer-generated numbers, patients were randomly allocated to cervical-mucus-removal (removed from both internal and external os) or non-mucus-removal groups. Only participants were blinded as to group assignment.Main outcome measures The clinical pregnancy rate.Results Of 714 IUI patients between November 2014 and March 2017, 361 were in the mucus removal group, and 353 in the nonmucus-removal group. Difficult catheterization was encountered in 17 cases out of 666 (2.6%) 12 in the cervical-mucus-removal group and five in the non-mucus-removal group). A total of 666 IUI cycles were completed while 48 were either cancelled or lost in their follow-up. The clinical pregnancy rate was significantly higher in the mucus-removal group [31.0% (n = 112)] than in the non-mucus-removal group [21.8% (n = 77); P = 0.005]. Ovarian hyperstimulation developed in 33 (4.6%) cases: 18 cervical mucus-removal and 15 non-mucus-removal. All except one were mild and managed with outpatient care.Conclusions Cervical mucus removal before IUI could improve pregnancy outcomes in women with unexplained infertility.