The aim of this study was to assess the behavior of fasting serum glucose, C-peptide levels and OGTT in pancreatic cancer follow-up. We studied 49 patients with pancreatic cancer (stage I = 8 pts; II = 16 pts; III = 12 pts; IV = 13 pts). At diagnosis 13/49 patients had fasting serum glucose levels of above 140 mg/dL. Of the remaining 36 pts, 22 underwent OGTT, which indicated diabetes mellitus in 9/22 (41%) and impaired glucose tolerance in 7/22 (32%) cases. C-peptide basal values were within the normal range (0.8-2.0 micrograms/L) in 14/49 (28%), above 2.0 micrograms/L in 6/49 (13%) and below 0.8 micrograms/L in 29/49 (59%) of the cases. No significant correlation was found between tumor stage or size and the presence of diabetes or of a reduced glucose tolerance. Twenty-four patients underwent curative resection (group 1) and 16 palliative resection, while the remaining nine did not undergo surgery (group 2). Group 1 and 2 patients had a follow-up of 2 to 40 months (mean = 14 months) and from 1 to 7.5 months (mean = 3.5 months) respectively. In group 1 patients no significant difference was found between pre- and post-operative fasting serum glucose levels. However, in 11/15 (73%) patients who underwent OGTT before and after surgery, an improvement in glucose tolerance was observed after tumor resection. In group 2 patients, a significant increase in fasting serum glucose levels was found during follow-up. In neither of the groups studied were significant variations found in C-peptide levels during the follow-up, although a slight increase was observed in patients who did not undergo surgery. In conclusion, the reduced glucose tolerance or frank diabetes mellitus, which frequently occurs during the onset of pancreatic cancer, does not seem to be related to tumor stage or size. Curative resection ameliorates glucose intolerance, while tumor persistence can enhance serum glucose levels.