Estrogen is associated with many epidemiologic risk factors for invasive breast cancer. Cells that express estrogen receptors (ERs) in epithelial hyperplasia lacking atypia (EHLA) may influence breast cancer progression. We conducted a nested case-control study of 268 women with biopsy-confirmed EHLA to determine whether immunohistochemical expression of ERα in EHLA affects subsequent breast cancer risk. Study subjects could not have a prior or current history of breast cancer or atypical hyperplasia. Immunohistochemical stains in individual lesions and adjacent normal lobules were considered positive if ≥ 10% of epithelial cells stained for ERα. The risk of invasive breast cancer in EHLA patients with ERα-positive normal lobules was twice that of other EHLA patients (95% CI = 1.0–3.8). This risk was not affected by the ERα status of EHLA lesions. ERα expression in adjacent normal lobules increases the moderate breast cancer risk previously associated with EHLA. © 2004 Wiley-Liss, Inc.