The Van Nuys Prognostic Index 1996 (VNPI), based upon tumor size, pathological grade and tumor margins, is a guideline for the treatment of ductal carcinoma in situ (DCIS). It was thought to strongly decrease overtreatment. In 2003, age was added to the index as a fourth prognostic factor. We examined changes in treatment modality after applying the VNPI retrospectively and investigated if the addition of age to the Index causes a shift in treatment. The influence of each prognostic factor on disease-free survival (DFS) was calculated. We performed a retrospective file study of DCIS patients treated between 1985 and 2003 at the University Hospital, Antwerp. Patients were assigned a Van Nuys Score 1996 and 2003. The influence of tumor size, pathological grade, tumor margins and age on DFS was calculated with the Kaplan-Meier method and the log-rank test. We identified 104 DCIS cases with a median follow-up of 36 months. Twelve patients showed recurrence (11.5%), of whom seven were invasive (58%). Seventeen of the 29 women diagnosed before 1997 were undertreated according to the VNPI 1996 and six of them showed recurrence. The remaining three recurrences were correctly treated. Seventy-five patients diagnosed after 1997 were all treated according to the VNPI 1996 and only three had a recurrence. The introduction of age caused no significant shift in treatment modalities. Significant differences in DFS were seen between large (>41 mm) and small (<15 mm) tumors (p = 0.0074), old (>60 years) and young (<40 years) patients (p = 0.024) and Van Nuys Subgroup 2 and 3 (p = 0.04). Tumor margins and pathological grade showed no significant difference in DFS. The VNPI can be a useful tool in the treatment of DCIS. However, this Index is not evidence-based, using a relatively small retrospective series of patients. The validity of the modified VNPI must be prospectively confirmed with large numbers of DCIS patients.