The aim of the present study was to assess criterion validity and external reliability of a questionnaire onrisk factors for breast cancer. Materials and Methods. Women with breast cancer diagnosis (the cases) (N=40)and matched individuals without cancer (the controls) (N=40) were asked to fill in a questionnaire twice: ona day of admission to hospital (Q1) and on a day before discharge (Q2), with a time interval of 4-6 days. Thequestionnaire included questions (N=150) on demographic and socioeconomic factors, diseases in the past,family history of cancer, woman’s health, smoking, alcohol use, diet, physical activity, and work environment.Criterion validity of the questionnaire Q2 relative to reference questionnaire Q1 was assessed with the Spearmancorrelation coefficient (SCC); external reliability of the questionnaire was measured in terms of the intraclasscorrelation coefficient (ICC). Statistical analysis was performed with SPSS 16. Results. The responses to most ofthe questions on socioeconomic factors, family history on cancer, female health, lifestyle risk factors (smoking,alcohol use, physical activity) correlated substantially in both the cases and the controls with SCC and ICC>0.7(p<0.01). Statistically non significant relationships defined only between the responses on amount of beer thecases drank at the ages up to 25 years and 26-35 years as well as time of use of estrogen and estrogens-progestinduring menopause by the cases. Moderate and substantial SCC and ICC were determined for different fooditems. Only the response of the cases on veal consumption did not correlate significantly. Conclusions. Thequestionnaire on breast cancer risk factors is valid and reliable for most of the questions included.