The development of an invasive recurrence following treatment for ductal carcinoma in situ (DCIS) converts a non-fatal disease to one associated with mortality. To date, no pathological or molecular features have been found to predict for the type of recurrence. Previous studies have suggested that in DCIS angiogenesis may be an important factor in determining the transformation from in situ to invasive carcinoma. We looked at 355 cases of DCIS and found that 32 had subsequently developed recurrent disease. In these 32 cases and in matched controls, periductal vascular density was determined using morphometry and anti-endothelial antibodies, von Willebrand factor (vWF) and CD34. Vascular density was related to the risk of both invasive and in situ recurrence. Normal lobules at least 2 mm away were used as controls. Differences in the phenotype of individual blood vessels was detected by performing dual staining immunofluorescence on selected cases. The microvessel density (MVD), as detected with the CD34 antibody, was higher around foci of DCIS than around normal breast lobules (P=0.001). Furthermore, it was significantly higher in cases of DCIS that recurred (P<0.0001). The findings with the vWF antibody were less clear cut and suggested a trend in decreasing MVD with increasingly aggressive disease. Dual immunofluorescence staining shows that the increase in MVD seen around DCIS is due to an increase in CD34+/vWF-blood vessels. An increase in CD34+/vWF-of blood vessels may be able to predict cases of DCIS that are at a high risk of developing a recurrence.