Prostate cancer is the most common malignant tumor in American men, yet only a small percentage of men will develop clinically significant disease. Needle core biopsies are used to confirm the presence of cancer prior to surgery. While needle core biopsies have shown some ability to predict tumor volume and grade in prostatectomy specimens, for the individual patient they are neither sensitive nor specific enough to guide therapy. In this paper, we describe a system for simulating needle biopsies on three-dimensional models of cancerous prostates reconstructed from serial sections. First we segment the serial sections, delineating tumors and landmarks. Next, we register the sections using a color-merging scheme, and reconstruct the three-dimensional model using modified shape-based interpolation. The resulting volume can be rendered, and simulated needle core biopsies can be taken from the reconstructed model. We use our system to simulate two different biopsy protocols on a reconstructed prostate specimen.