The University of Southern California/Van Nuys Prognostic Index is an algorithm that quantifies five measurable prognostic factors known to be important in predicting local recurrence in conservatively treated patients with ductal carcinoma in situ (tumor size, margin width, nuclear grade, age, and comedonecrosis). With three times as many patients since originally developed, sufficient numbers now exist for analysis by individual scores rather than groups of scores. To achieve a local recurrence rate of less than 20% at 12 years, these data support excision alone for all patients scoring 4, 5, or 6 and patients who score 7 but have margin widths ≥ 3 mm. Excision plus RT achieves the less than 20% local recurrence requirement at 12 years for patients who score 7 and have margins < 3 mm, patients who score 8 and have margins ≥ 3 mm, and for patients who score 9 and have margins ≥ 5 mm. Mastectomy is required for patients who score 8 and have margins < 3 mm, who score 9 and have margins < 5 mm, and for all patients who score 10, 11, or 12 to keep the local recurrence rate less than 20% at 12 years. These recommendations in this article represent substantial changes from those previously published.