We evaluated established risk factors (tumor size, lymph node status, menopausal status, estrogen receptor status, tumor histology and grading according to Bloom and Richardson, including subfactor analysis), as well as the influence of local procedures, in 138 patients with primary carcinoma of the breast smaller than 1 centimeter. The patients were operated upon during 1969 to 1989 at the Department of Surgery, Hanusch Medical Center, Vienna. Twenty-two patients had a recurrence after a median observation time of 15 years. Seven patients died of the primary disease by the control date (31 May 1990). Grading (p = 0.01, 0.0044) as well as nuclear polymorphism (p = 0.003, 0.00001) and mitosis rate (p = 0.02, 0.01) proved to be significant parameters for recurrence free survival and overall survival. Local procedures (modified radical mastectomy, breast conserving operation with or without postoperative radiotherapy) revealed borderline significance with local recurrence free survival (p = 0.08). All other parameters were without any statistical significance (Mantel-Cox log rank test). Our data confirm the superior prognostic relevance of histologic grading and nuclear polymorphism in patients with carcinoma of the breast smaller than 1 centimeter. High grade nuclear polymorphism as a subfactor in the grading classification according to Bloom and Richardson appears to be a highly valid risk factor for this entity.