A random sample of 2266 women aged 50 to 69 years was used to investigate factors that predict attendance at a free Australian mammographic screening program. The most important predictor was receipt of a personal invitation letter. A letter that included an appointment time increased attendance 132-fold initially and decreased to 20 times baseline after 14 days. A letter that did not include an appointment time increased attendance 12-fold, and a second letter to nonattenders increased attendance approximately 13-fold. Attendance declined with increasing distance from the program and with increases in the percentage of non-English speaking women in a neighborhood, but was higher in areas of higher socioeconomic status.