METHODS. A randomized pretest post-test control group design was used to evaluate the effectiveness of a mail-out intervention for increasing screening mammography rates. A random sample of 802 women, 40+, residing in Los Angeles County, was surveyed by telephone at baseline and again 12 months after the intervention. RESULTS. Fifty percent of the intervention group and 56% of the control group had obtained a screening mammogram during the follow-up period. This difference was not statistically significant, indicating that the low-cost intervention was not successful in influencing screening mammography rates in this sample. In the combined intervention and control group, a stepwise logistic regression analysis revealed four baseline variables to be significant prospective predictors of mammography behavior during the follow-up period: Women who were adherent to the age-specific screening guidelines at baseline and women who had health insurance were more likely to obtain a mammogram during the follow-up, as were older women. Also, women who were greatly concerned about radiation exposure during a mammogram were about two and a half times less likely to obtain a mammogram during the follow-up than women who were less concerned. Self-reported reasons for adherence and nonadherence to screening guidelines are also described.