Purpose Bile duct brushings (BDB) have low diagnostic sensitivity, negative predictive value and no known prognostic information. We aimed to assess the diagnostic and prognostic performance of BDB and identify clinicopathological factors associated with false-negative BDB. Methodology BDB at Christchurch hospital between January 2018 to March 2024 were retrospectively identified. Patient history, biochemical markers, radiology, management and outcomes were analysed. BDB were categorised according to WHO guidelines. Results Of 418 BDB, 7 (1.7%) were insufficient, 231 (55.3%) benign, 33 (7.9%) atypical, 7 (1.7%) pancreaticobiliary neoplasm, 21 (5.0%) suspicious for malignancy and 119 (28.5%) malignant. Final diagnoses were 156 (37.3%) benign, 157 (37.6%) pancreatic adenocarcinoma, 64 (15.3%) cholangiocarcinoma, 8 (1.9%) ampullary adenocarcinoma, 7 (1.7%) pre-malignant and 26 (6.2%) other malignancies. 140 BDB were true positives, 0 false positives, 117 false-negatives (FN) and 161 true negatives (TN) giving sensitivity 54.5%, specificity 100%, PPV 100% and NPV 57.9%. Compared with TN, FN patients were older (median 73 vs 68 years, p<.001) and more likely to have metabolic disease (59.8% vs 37.7%, p<.001), but less likely to have a history of pancreatitis (8.5% vs 17.0%, p=.030), prior cholangitis (0.9% vs 7.5%, p=.007) or alcohol dependence (0.9% vs 9.4%, p=.003). 42 patients underwent surgery; 6 and 20-month survival rates of 98% and 42% respectively. Comparing those alive at 20 months (20m-A) with those deceased by 20 months (20m-D), bilirubin and CA19-9 did not differ; however, malignant BDB cytology was more frequent in 20m-D (76.5%), whereas benign cytology was more frequent in 20m-A (48.0%) (p=.030). Conclusion BDB has high specificity but limited sensitivity for indeterminate biliary strictures, with false negatives associated with distinct patient factors. WHO BDB cytology categories also appear to stratify survival, suggesting potential prognostic value.