OBJECTIVE: The purpose of this prospective study was to compare the performance of (111)In-octreotide somatostatin receptor scintigraphy (SRS) and (18)fluorodesoxyglucose positron emission tomography (FDG-PET) in aggressive well-differentiated endocrine carcinoma (WDEC) defined by a high Ki67 (>/=10%). METHODS: Eighteen consecutive patients explored in a single hospital between November 2003 and 2008 for high Ki67 (>/=10%) WDEC were prospectively included. WDEC were sporadic in 17 cases and secreting in 16 cases. FDG-PET, SRS, and computed tomography (CT) were performed within a maximum of 3 months and reviewed by two independent readers. For each patient, an analysis per organ and lesion was performed. Both the results of conventional imaging and the highest number of metastatic organs and distinct lesions visualized by all imaging methods including SRS, FDG-PET, and thoraco-abdomino-pelvic CT were considered for the determination of the standard. Correlation between tumor slope and maximum standardized uptake value, Ki67 value, and grade of uptake at SRS was evaluated. RESULTS: FDG-PET, SRS, and CT showed at least one lesion in 18 (100%), 15 (83%), and 17 (94%) patients, respectively. A total of 254 lesions were diagnosed in 59 organs. FDG-PET, SRS, and CT detected 195 (77%), 109 (43%), and 195 (77%) lesions in 53 (90%), 30 (51%), and 39 (66%) organs, respectively. FDG-PET, compared to SRS, detected more, the same as, and less lesions in 14 (78%), one (6%), and three (17%) patients, respectively. A statistical trend was found between Ki67 value and tumor slope (P = 0.07). Median survival after diagnosis was 25 months (range, 6-71 months). CONCLUSION: These results suggest that FDG-PET is more sensitive than the SRS for high Ki67 WDEC staging.