The aim of this study was to compare the age-standardised incidence rates of gastric bowel and pancreatic cancer between two regions of the Republic of Croatia: (1) five middle Dalmatian islands (Brac, Hvar, Korcula, Vis and Lastovo) with "Mediterranean" nutrition; (2) the control population of Koprivnicko-krizevacka County (KKC) with "continental" nutrition. The characterisation of nutrition habits in the two study regions revealed very significant differences. The newly registered cases of gastric, bowel and pancreatic cancer between 1986 and 1995 were retrieved from the Cancer Registry of Croatia. The resulting incidence rates were standardised to the standard world population using the method of direct standardisation. Age-standardised incidence rates in the islands in comparison to the control KKC population per 100,000 inhabitants were 17.2 vs. 39.4 (p < 0.001) in males with gastric cancer, 9.1 vs. 16.5 (p < 0.01) in females with gastric cancer, 34.5 vs. 31.4 (p > 0.05) in males with bowel cancer, 18.3 vs. 20.3 (p > 0.05) in females with bowel cancer, 5.5 vs. 9.0 (p < 0.05) in males with pancreatic cancer and 2.7 vs. 5.0 in females with pancreatic cancer (p < 0.05). Standardised incidence rates of gastric and pancreatic cancer in the island populations were significantly lower from the standardized Croatian average. The study showed that "Mediterranean" type of diet could have a protective effect against gastric and pancreatic cancer.