It has been suggested that early-onset breast carcinomas may be different from those that occur in older women. The clinicopathologic characteristics of 191 young female patients (under 40 years of age) diagnosed with breast carcinoma (BC) were studied. Clinical history, staging, treatment and outcome were reviewed. Histology was assessed for tumor subtypes, invasive and in situ components, nuclear and histologic grades and lymph node status. Adjacent nontumoral breast tissue was evaluated. Clinically, 11 patients were stage 0, 21 stage I, 94 stage II, 38 stage III, 6 stage IV, and in 21 no information was obtained. Sixty five percent of patients had positive lymph nodes at diagnosis; 102 patients (54%) relapsed at a median of 29 months after diagnosis. Histologically, 180 cases were infiltrating BC, 150 ductal (83%), 19 lobular (11%) and 11 of special types (6%); 11 cases were ductal carcinoma in situ. We found no cases of medullary carcinoma. High nuclear grade and vascular invasions were frequent (68% and 67%, respectively) even in patients who remained disease-free at least 5 years after diagnosis (61% and 60%, respectively). Our study demonstrates that the histologic types of early-onset breast cancer are not different from other BC. However, BC in young women is often associated with histologic features of high-grade malignancy even in patients with better survival. Our results suggest that BCs in young women are different from those that occur in older women.