The DNA ploidy of pancreatic cancer tissue from paraffin blocks was measured by flow cytometry in 46 patients whose disease had been detected and treated with surgery. Lymph node involvement was observed at the time of diagnosis in 36% of patients with diploid tumors and in 79% of patients with aneuploid tumors (p = 0.017), but no clear relation to metastasis could be observed (p = 0.201). The S-phase fraction (SPF) was significantly higher in aneuploid than in diploid tumors (p = 0.007). All patients who underwent radical surgery had diploid DNA content and SPF below the median (11.5%). Seven patients with a diploid tumor (32%) and none of the aneuploid cases survived 1 year. Over the 1-year period, in order of importance, the type of treatment (p less than 0.001), DNA ploidy (p = 0.004), tumor size (p = 0.0046), and lymph node status (p = 0.027) predicted survival. Aneuploidy showed a significant association with decreased cumulative survival (p = 0.015), and a suggestive relationship with SPF was found. The results suggest that DNA ploidy of pancreatic cancer can be used in dividing the patients into different prognostic groups. The value of the detection of aneuploidy, however, is limited, because diploid pancreatic cancers are also generally rapidly fatal.