Aneuploidy in pancreatic insulinomas does not predict malignancy. Nuclear deoxyribonucleic acid (DNA) ploidy studies with paraffin embedded archival material from 14 pancreatic insulinomas were performed by flow cytometry. Clinical follow-up (2 to 17 years; mean, 8 years) was obtained for all patients. Half of the tumors had a normal DNA histogram and half exhibited an abnormal DNA profile consistent with DNA aneuploidy. Six of the seven patients with aneuploid tumors are alive and disease free (2 to 5 years postresection), and one is alive with metastatic disease. Of the seven patients with tumors showing normal DNA profiles, five are alive and disease free, one is dead of disease, and one is alive with metastatic disease. These data suggest that DNA ploidy analysis is unlikely to provide useful prognostic information for patients with insulinomas. 