We considered the role of monounsaturated and other types of fats on breast carcinogenesis, using data from a case-control study of 2,569 incident, histologically confirmed cases of breast cancer and 2,588 controls from six Italian areas. The multivariate odds ratios, adjusted for age, education, parity, menopausal status plus various sources of energy and types of fats, were 1.10 (95% confidence interval 0.99-1.23) for an increase of 10 g/day of saturated fat intake, 0.99 (0.94-1.04) for an increase of 10 g/day of monounsaturated fats, and 0.91 (0.87-0.96) for an increase of 5 g/day of polyunsaturated fats. The present data confirm that saturated, but not mono- or polyunsaturated fats, are directly, though moderately, related to breast cancer risk.