We examined the effect of preoperative chemoradiotherapy on the ability to obtain pathologically negative resection margins in patients undergoing pancreaticoduodenectomy for adenocarcinoma of the head of the pancreas. Between 1987 and 2000, 100 patients underwent Whipple resection with curative intent for primary adenocarcinoma of the head of the pancreas. Pathologic assessment of six margins (proximal and distal superior mesenteric artery, proximal and distal superior mesenteric vein, pancreas, retroperitoneum, common bile duct, and hepatic artery) was undertaken by either frozen section (pancreas and common duct) or permanent section. A margin was considered positive if tumor was present less than 1 mm from the inked specimen. Margins noted to be positive on frozen section were resected whenever possible. Of the 100 patients treated, 47 (47%) underwent postoperative radiation and chemotherapy (group I) and 53 (53%) received preoperative chemoradiotherapy (group II) with either 5-fluorouracil (32 patients) or gemcitabine (21 patients). Patient demographics and operative parameters were similar in the two groups, with the exception of preoperative tumor size (CT scan), which was greater in group II (P < 0.001), and number of previous operations, which was greater in group II (P < 0.0001). Statistical analysis of the number of negative surgical margins clear of tumor was performed using Fisher's exact test. All patients (100%) had six margins assessed for microscopic involvement with tumor. In the preoperative therapy group, 5 (7.5%) of 53 patients had more than one positive margin, whereas 21 (44.7%) of 47 patients without preoperative therapy had more than one margin with disease extension (P < 0.001). Additionally, only 11 (25.6%) of the 47 patients without preoperative therapy had six negative margins vs. 27 (50.9%) of 53 in the group receiving preoperative therapy (P = 0.013). Survival analysis reveals a significant increase in survival in margin-negative patients (P = 0.02). Similarly, a strong trend toward improved disease-free and overall survival is seen in patients with a single positive margin vs. multiple margins. Overall, we find a negative impact on survival with an increasing number of positive margins (P = 0.025, hazard ratio 1.3). When stratified for individual margin status, survival was decreased in patients with positive superior mesenteric artery (P = 0.06) and vein (P = 0.04) margins. However, this has not yet resulted in a significant increase in disease-free or overall survival for patients receiving preoperative therapy (P = 0.07).