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BACKGROUND: Intraductal papillary mucinous neoplasms (IPMNs) are pre-malignant pancreatic cysts detected by imaging. Cyst size is one of many features evaluated on computed tomography (CT), magnetic resonance imaging (MRI), or endoscopic ultrasonography (EUS) to help guide IPMN management. Our objective was to determine which imaging modality best predicts pathological cyst size. METHODS: We analyzed records for 57 IPMN cases surgically treated at Moffitt Cancer Center from 2008-2016 for whom pre-operative CT, MRI, and EUS IPMN cyst size and post-operative pathological cyst size values were available. Long axis cyst diameter measurements were compared to each other and corresponding pathological cyst measurements using within-subjects ANOVA, Bland-Altman analysis, and linear regression. Consensus measurements were also performed on CT and MRI images. RESULTS: Cyst size measured via CT and MRI overestimated pathological size by 0.33 cm and 0.27 cm, respectively, whereas EUS underestimated pathological size by 0.05 cm and had the narrowest 95% limit of agreement (LOA). Among pathologically-confirmed cysts < 3 cm, MRI overestimated pathological size by 0.30 cm (P=0.049) and had the widest LOA, followed by EUS and CT. Among cysts ≥3 cm, EUS underestimated pathological size by 0.35 cm (P=0.059) and MRI and CT overestimated pathological size by 0.23 cm and 0.51 cm, respectively. CONCLUSIONS: In this small retrospective study, EUS cyst size measurements correlated best with pathologic specimens compared to CT and MRI, especially for cysts < 3 cm. Larger prospective studies are needed to determine which imaging modalities are best to risk-stratify IPMNs and guide surgical versus. non-surgical management.