Intracholecystic papillary neoplasm (ICPN) is a preinvasive neoplasm of the gallbladder that grows as an intraluminal papillary or polypoid lesion, but its imaging features have not been sufficiently characterized. The case presented here uniquely demonstrates the natural history of ICPN, documented by serial computed tomography over a two-year period during postoperative surveillance for renal cell carcinoma. A 63-year-old man was found to have a slowly enlarging hyperdense intraluminal gallbladder mass on unenhanced computed tomography (CT). Retrospective review demonstrated gradual growth over approximately two years. The lesion measured 45 mm in diameter and showed persistent enhancement from the early arterial phase through the equilibrium phase on dynamic contrast-enhanced CT. Magnetic resonance imaging revealed a papillary mass; T2-weighted imaging demonstrated mildly increased signal intensity within the soft-tissue component, and diffusion-weighted imaging showed diffuse mild hyperintensity throughout the tumor. Despite the large size, there were no imaging findings suggestive of advanced gallbladder carcinoma, such as irregular thickening of the gallbladder wall, extramural invasion, or metastatic disease. The patient underwent laparoscopic cholecystectomy. Histopathological examination demonstrated glandular proliferation with high-grade cytologic atypia and diffuse MUC6 positivity, consistent with gastric non-mucinous type ICPN with associated high-grade intraepithelial neoplasia. ICPN should be considered in the differential diagnosis of a papillary intraluminal gallbladder tumor that lacks clear evidence of invasion on imaging.