Abstract: This study aimed to assess the effect of reminder letters on Pap test rates for women enrolled on the New South Wales Cancer Council Pap Test Reminder Service and to identify predictors of response to the letter. Ten weeks after they had received their reminder letter a questionnaire was sent to 3086 women. It was completed by 1525 (49 percent) women, of whom 1393 (91 percent) said they had received their reminder letter. Of these 1393, 48 per cent (95 per cent confidence interval 46 per cent to 51 per cent) reported having had a Pap test within 10 weeks of the reminder letter arriving. The proportion of women having a Pap test in response to the reminder letter did not differ by age, region of residence or language spoken at home. Women were less likely to have had a Pap test if they did not know how they were enrolled, were of low socioeconomic status or had some tertiary education. Women on the reminder service have 15-month rescreening rates at least 9 per cent higher than other women in New South Wales; for women aged 50 to 69 in nonmetropolitan areas the increase is estimated at 19 per cent. Reminder services may be a cost-effective way to increase Pap test rescreening rates. Reminder services need accurate records and to follow up changes in address and date of next test.