The hypothetical multistep model of carcinogenesis indicates that breast cancer develops via a series of intermediate hyperplastic lesions through in situ to invasive carcinoma. To identify the risk inherent within the different morphologic lesions, we have analyzed the data from 674 benign biopsy specimens comprising 120 cases who subsequently developed breast cancer and 382 controls (matched for age and date of biopsy) spanning a period up to 20 years of follow-up (mean 66.95 months). In this series we have confirmed an increased risk associated with certain types of benign breast lesions. Atypical lobular hyperplasia was the most significant risk factor for breast cancer with more unfavorable outcome in patients <50 years of age (p = 0.003) and a relative risk (RR) of 4.55 (confidence interval [CI] 1.77-11.69). Hyperplasia of usual type showed an RR of 1.53 (CL 1.10-2.13) with a statistically worse probability of survival (cancer-free time) for patients >50 years. For atypical ductal hyperplasia the RR was 2.03 (CI 0.80-1.39). Blunt duct adenosis was significantly more common in cases progressing to breast cancer compared with controls, showing an RR of 2.08 (CI 1.12-2.85). We describe in detail the criteria of morphologic changes observed in blunt duct adenosis and define, for the first time, the level of risk associated with each of its six subtypes. Improved knowledge of breast carcinogenesis will provide insight for defining high-risk groups thus resulting in improved screening and management regimens.