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To determine the prognostic influence of residual tumor at or within 1 mm of the mobilization margins (R1Mobilization) compared with transection margins (R1Transection) following pancreaticoduodenectomy for pancreatic ductal adenocarcinoma (PDAC).The prognostic strength of R1 status increases with frequency of margin positivity and is enhanced by protocol driven pathology reporting. Currently, margins are treated uniformly with tumor at or close to any margin considered of equal prognostic significance. The resection involves a mobilization phase freeing the posterior margin and anterior surface then a transection phase requiring lympho-vascular division forming the medial resection and pancreatic transection margin. The comparative assessment of the relative importance of tumor involvement of these different margins has not previously been investigated.Retrospective analysis of 148 consecutive resections for PDAC from 1996–2007 was performed. The individual (pancreatic transection, medial, posterior, and anterior surface) margins were separately identified and analyzed by a senior pathologist. An R1 resection was defined as microscopic evidence of tumor ≤1 mm from a resection margin. R1Mobilization tumor extension included both R1Anterior and R1Posterior cases; while R1Transection included pancreatic neck/body transection, R1Medial and adjacent transection margins.R1 status was confirmed in 109 patients (74%). The medial (46%) and posterior (44%) margins were most commonly involved. R1 status was found to an independent predictor of poor outcome (P < 0.001). R1Mobilization involvement only (n = 48) was associated with a significantly longer median survival of 18.9 months (95% CI, 13.7–24.8) versus 11.1 months (95% CI, 7.1–15.0) for those with R1Transection tumor involvement (n = 61) (P < 0.001). There was no significant difference in the survival of the R1Mobilization compared with R0 group (P = 0.52).Following pancreaticoduodenectomy for PDAC, involvement of the transection margins in contrast to mobilization margins defines a group whose outcome is significantly worse. This may impact upon the allocation of adjuvant therapy within the setting of randomized controlled trials.