BACKGROUND: The purpose of this study was to evaluate the tumor biology with respect to bilaterality and recurrence rates for bilateral infiltrating lobular (IL) breast carcinoma in comparison with other histological types. METHODS: A prospectively accrued data base containing 1,548 breast cancer cases as well as H. Lee Moffitt Cancer Center's cancer registry compiled during the same period were queried for specific features relating to bilaterality and recurrence. The 116 patients in this study had been treated at the Comprehensive Breast Cancer Clinic and had documented bilateral breast cancer (invasive on situ). RESULTS: Eighty-two of the patients (70.7%) had metachronous breast cancer, and 34 (29.3%) had synchronous cancer. Although median follow-up times were short, the risk of developing breast cancer in the contralateral breast after the diagnosis of cancer in the ipsilateral breast was estimated to be 0.7% per patient-year of follow-up. Recurrence rates for IL cancers were compared with those for invasive ductal (ID) and for ID + IL cancers. IL cancers recurred 8.1% of the time, whereas ID cancers recurred at a rate of 7.8%. Recurrences were equally divided between local and distant sites. CONCLUSIONS: Although IL cancers have demonstrated insidious behavior, their incidence of bilaterality is only slightly higher than other histologies and their rates of recurrence are low when properly evaluated and treated. The risk to the opposite breast also appears to be low. These data do not support the routine use of blind contralateral biopsy or prophylactic mastectomy.