BACKGROUND Ovarian cancer, one of the most common cancers in women and the most serious gynecologic cancer, is known to be influenced by reproductive factors, but these factors have not previously been examined in Vietnamese women. STUDY DESIGN We analyzed 262 ovarian cancer patients recruited from 27 hospitals in 12 provinces and Ha Noi City from April 2001 to May 2006, plus 755 controls matched by age and residential address. RESULTS The risk of ovarian cancer was significantly lower in parous women than nulliparous women. Use of an intrauterine contraceptive device was also associated with a reduced risk. In contrast, induced abortion, late menopause and years of ovulation were significantly associated with an increased risk of cancer. CONCLUSIONS Parity and intrauterine device use were associated with a reduced risk of ovarian cancer in Vietnamese women, whereas induced abortion, late menopause and years of ovulation were associated with an increased risk.