To prove the effectiveness of mass screening for cervical cancer with the cervical cytologic smear in Japan. The cases consisted of 109 patients with invasive carcinoma who were identified by mass screening for cervical cancer between 1984 and 1989. For each case, two age-matched controls were chosen from females who underwent mass screening in the same district during the same period. The odds ratio (OR) for invasive cervical cancer and that of each histologic type for the previously screened vs. unscreened females were calculated. In addition, the OR for invasive cervical cancer according to the screening interval was calculated. The OR of invasive cervical cancer for the previously screened vs. unscreened females was significant (P < .16). According to the histologic type, the OR of squamous cell carcinoma for the previously screened vs. unscreened females was significant (P < .14), while that for adenocarcinoma was not significant (P < .45). According to screening interval, the OR for screening at a one- or two-year interval was significant (P < .11 and .33, respectively). This case-control study statistically showed the usefulness of screening for cervical cancer in Japan.