OBJECTIVE To investigate the effectiveness of mass screening for endometrial cancer using Endocyte (Laboratoire CCD, Paris, France) endometrial smears. STUDY DESIGN The study subjects were consecutive patients with documented endometrial cancer diagnosed between January 1, 1989, and December 31, 1997, at 22 hospitals in Japan. One hundred twenty-six cases were detected by mass screening and 1,069 diagnosed in outpatient clinics. We compared the stage of cancer at diagnosis and survival rate of patients in the two groups. RESULTS Early stage was significantly more frequent in the screening group (P < .001); stage I comprised 88.1% of the screening group as compared with 65.3% of the outpatient group. Well-differentiated adenocarcinoma was significantly more frequent in the screening group (P < .01); grade 1 constituted 74.7% of the screening group as compared with 61.0% of the outpatient group. The five-year survival rate was significantly higher in the screening group than in the outpatient group (94.0% vs. 84.3%, P = .041). The crude hazard ratio (HR) of dying of endometrial cancer for the screening group as compared to the outpatient group was .47 (95% CI .22-.99, P = .048). HR became .96 (95% CI .45-2.08, P = .925) after adjustment for age, study area and cancer stage. CONCLUSION The results suggest that an endometrial cancer screening program would lead to early detection and improved survival among women with endometrial cancer.