Objective The aim of this study was to develop a measurement instrument for assessing knowledge of breast cancer and perceived risk of developing the disease (MARA). Methods 641 women with a mean age of 36.19 years (SD = 7.49) was used. Data collection took place during 2019 and included sociodemographic data, data on history of cancer and breast cancer and perceived risk and feelings of concern about developing breast cancer. Internal consistency, test-retest reliability, convergent validity, and structural validity were tested. Results The questionnaire items comprise 4 subscales: risk factors; signs and symptoms; perceived risk; barriers. A factor analysis revealed that the first two subscales had two dimensions each, whereas the other two subscales had one dimension each. Each subscale was shown to have adequate reliability (α = 0.74–0.92) and temporal stability (r = 0.201–0.906), as well as strong evidence of validity in relation to a questionnaire on breast cancer knowledge (r = 0.131–0.434). In addition, the subscales were shown to have high discriminatory power in terms of the presence or absence of a history of cancer or breast cancer, perceived risk, and feelings of concern. Conclusion The MARA questionnaire exhibits adequate psychometric properties for assessing knowledge of breast cancer as required in research and professional contexts.