Background and Study Aims: Brush cytology of biliary strictures has a low sensitivity for diagnosing malignancy, and additional diagnostic tools are needed. The aim of the present study was to assess the diagnostic and prognostic importance of DNA measurements as an adjunct to brush cytology in patients with biliary strictures. Patients and Met hods: All patients (n=225) with bile duct strictures who underwent endoscopic retrograde cholangiopancreatography(ERCP) between January 1997 and October 2003 at the Department of Radiology at Karolinska University Hospital, Huddinge, Sweden, were included in the study. While 66 patients had an unclear final diagnosis and were therefore excluded, the remaining 159 patients were assessed with brush cytology and DNA flow cytometry. Results: Sensitivity and specificity of DNA aneuploidy for tumor detection were 43%and 96%. Using DNA analysis in addition to brush cytology, the sensitivity was 62%compared with 57%for brush cytology alone (not significant). Patients with diploid DNA tumors had a significantly better survival than patients with aneuploid DNA tumors (P=0.02). The mean survival was 10 months for diploid cancers and 6 months for aneuploid cancers. Conclusion: DNA ploidy measurement may be a diagnostic method that could supplement brush cytology in the identification of malignancy in biliary strictures. DNA aneuploidy is a marker of poor prognosis in patients with malignant biliary strictures. Background and Study Aims: Brush cytology of biliary strictures has a low sensitivity for diagnosing malignancy, and additional diagnostic tools are needed. The aim of the present study was to assess the diagnostic and prognostic importance of DNA measurements as an adjunct to brush cytology in patients with biliary strictures. Patients and Met hods: All patients (n = 225) with bile duct strictures who underwent endoscopic retrograde cholangiopancreatography (ERCP) between January 1997 and October 2003 at the Department of Radiology at Karolinska University Hospital, Huddinge, Sweden, were included in the study. While 66 patients had an unclear final diagnosis and were caused excluded, the remaining 159 patients were assessed with brush cytology and DNA flow cytometry. Results: Sensitivity and specificity of DNA aneuploidy for tumor detection were 43% and 96%. DNA analysis in addition to brush cytology, the sensitivity was 62% compared with 57% for brush cytology alone (not signific ant). Patients with diploid DNA tumors had a significantly better survival than patients with aneuploid DNA tumors (P = 0.02). The mean survival was 10 months for diploid cancers and 6 months for aneuploid cancers. Conclusion: DNA ploidy measurement may be a diagnostic method that could supplement brush cytology in the identification of malignancy in biliary strictures. DNA aneuploidy is a marker of poor prognosis in patients with malignant biliary strictures.