In signet-ring cell carcinoma of the breast, which was recognized in 1976 as a distinct clinicopathologic variant of lobular carcinoma, more than 20% of the malignant cells appear as signet rings formed by mucin-positive intracytoplasmic vacuoles. Several recent studies have demonstrated that the neoplasm behaves aggressively and is associated with a poor prognosis. However, the literature lacks information concerning steroid hormone receptor assays and DNA ploidy profiles, especially regarding how these tests affect a patient's prognosis. During a 5-year period (1985 to 1990), 11 (8.7%) of 126 cases of invasive lobular carcinoma met the criteria for signet-ring cell carcinoma. Ten of 11 cases were positive for estrogen and progesterone receptors; six cases showed type I and five showed type III DNA histograms. The high incidence of positive hormone receptors is significant: patients with receptor positive tumors, even those with type III DNA histograms, who were treated with tamoxifen citrate therapy after surgery had a significant increase in disease-free survival (30 months). Both the pathologist and the clinician should be aware of the prognostic influence of hormone receptor studies in the management of signet-ring cell carcinoma of the breast.