This study aimed to determine the value of CT, endoscopic sonography, and a combined protocol for preoperative detection of insulinomas. All patients treated in our institution for surgically proven insulinoma between 1987 and 2000 were retrospectively reviewed. Thirty patients with 32 pancreatic insulinomas underwent preoperative CT and endoscopic sonography and were included in the study. These 30 patients also underwent dual-phase thin-section multidetector CT (group 1: n = 15), dual-phase multidetector CT without thin sections (group 2: n = 8), or sequential CT (group 3: n = 7). CT scans were interpreted separately and retrospectively by three radiologists in consensus. Sensitivity values for CT, endoscopic sonography, and a combined protocol were determined. The overall diagnostic sensitivity for dual-phase helical CT was 94.4% for group 1, 57.1% for group 2, and 28.6% for group 3. Endoscopic sonography showed proven insulinomas in 30 of 32 cases (sensitivity, 93.8%). Differences between dual-phase thin-section CT and endoscopic sonography were not statistically significant. The overall diagnostic sensitivity for combined biphasic thin-section helical CT and endoscopic sonography was 100%. The most effective method for revealing insulinomas is a combined imaging protocol that consists of both dual-phase thin-section multidetector CT and endoscopic sonography.