The goal of the present study is to evaluate HDL-cholesterol (HDL-C) as a marker of breast cancer (BC) risk. It is based on several epidemiological and biological studies and is justified by the rising incidence of breast cancer throughout the world. A hospital-based study on host-related risk factors and breast cancer, conducted with similar methods in northern Italy and southern France, provided the biological data, the information on the established BC risk factors and on nutrition for 307 cases and 329 controls. This data set allowed for a thorough analysis of the relationship of HDL-C with established risk factors for BC and also of its association with BC at the time of diagnosis. Most of our findings on HDL-C determinants in the control sample are comparable to previous studies. The BC risk factors associated with reproductive life correlate with HDL-C levels: the protective factors are associated with a lower level of HDL-C and inversely. The same is true for nutritional factors such as alcohol. For these determinants, the trend is similar for cases and controls, and HDL-C level appears to be related to oestrogen metabolism. Thus it may be considered as a marker of BC risk. Our results indicate that high HDL-C levels should be especially checked in women aged > or = 60 years, or in premenopausal women presenting a low BMI, or in postmenopausal women with an early menopause.