A precise histologic and clinical delineation of infiltrating lobular carcinoma, including its variant forms, has been elusive. We studied 230 patients with stage I and II infiltrating lobular carcinoma treated by mastectomy and axillary lymph node dissection. Included were 176 patients with the "classical" or "Indian-file" pattern (IFL) of infiltrating lobular carcinoma, and 54 patients with variant (VAR) histology [solid (SOL), alveolar (ALV), and mixed (MIX) patterns]. IFL patients were younger than VAR patients (52 versus 57 years; p = 0.004), and IFL patients were more likely to be premenopausal (p = 0.013). Microscopic multifocality and intraepithelial ductular extension of LCIS were both more frequent in the IFL group (p = 0.008 and 0.03, respectively). There was no significant difference in tumor size (T1 versus T2), axillary lymph node status, or TNM stage at presentation. Median survival time and time to recurrence was similar in the two groups. Although it was not statistically significant, median survival for stage I and low-axillary lymph node positive stage II IFL patients was better than that of VAR patients. One hundred forty of our 176 IFL patients (80%) could be matched with infiltrating duct carcinoma (IFDC) patients of similar age at diagnosis, menstrual status, tumor size, and axillary lymph node involvement. When stratified by stage, stage I IFL patients had a significantly higher disease-free survival (p = 0.02) than comparable patients with IFDC. There was not a significant difference in disease-free survival when stage II IFL and IFDC patients were compared. The unmodified term "infiltrating lobular carcinoma" should be restricted to lesions exhibiting the classical or Indian-file (IFL) microscopic architectural pattern in approximately 85% of the tumor. Patients with VAR forms of IFL may have a less favorable prognosis and should be distinguished from those with classical IFL for further characterization.