Objectives: In this study, it was aimed to compare the knowledge, attitudes and awareness of women with and without SMI towards breast cancer. Methods: This comparative, cross-sectional study was conducted between March and December 2024 with 109 women with SMI and 109 women without SMI in western of Turkey. The Breast Cancer Awareness Scale was used to measure knowledge, attitudes, and awareness regarding breast cancer. A non-probability sampling method was used. Breast cancer awareness among women with and without SMI was analyzed using the student's t-test. Results: The mean breast cancer awareness scale score was 0.61 +/- 0.67 for women with SMI and 1.05 +/- 0.61 for women without SMI. It was found that women with and without SMI had low breast cancer awareness levels, but those without SMI had statistically significantly higher breast cancer awareness than women with SMI (p < 0.001). It has been determined that women without SMI have higher breast cancer awareness scores than women with SMI, based on marital status, employment status, educational status, income status, childbearing status, body mass index, and smoking status. Implications for practices: It is recommended to determine the factors affecting the low knowledge, attitude and awareness of breast cancer in women with and without SMI and to carry out interventions to increase their knowledge, attitude and awareness of breast cancer.