Objective: Some Japanese institutes have been performing a population screening program for cervix cancer involving the simultaneous use of Pap smear and colposcopy. This program may be a good model for evaluating the efficacy of Pap smears and colposcopy. Methods & Materials: The subjects included 2,000 women who underwent primary screening at the Kanagawa Health Service Association. Results: 1) The incidence of ACF (atypical colposcopic findings) was 3.6%, whereas that of abnormal Pap smears (ASC-US and above) was 1.1%; 2) Of 88 women who showed abnormal findings on Pap smear and/or colposcopy, only three cases appeared abnormal in both methods, i.e., the two methods were complementary; 3) Colposcopy was more useful for detecting mild dysplasia than the Pap smear. However, colposcopy may possibly detect benign reparatory lesions; 4) The incidence of unsatisfactory colposcopic findings (UCF) was high (24.2%), whereas no unsatisfactory cases were found by Pap smear. Conclusions: The sensitivity of the Pap smear for detecting mild dysplasia is low, whereas that of colposcopy is high. However, colposcopy may not be suitable for primary screening due to its high UCF. The low sensitivity of Pap smears may be improved by repetition or adding ancillary HPV testing.