Results: Cytology: Large and small round-shaped tumor cells were present with round nuclei with granular chromatin. Double-or triple-nucleated cells and amyloid material were observed. Histology: oncocytic round cells proliferated diffusely in the fibrous capsule. Extra-capsular invasion and vascular infiltration by the tumor cells were recognized. Electron microscopy: the cytoplasm of tumor cells was full of mitochondria. Therefore, we diagnosed this as follicular carcinoma, oncocytic variant. Amyloid deposition was also observed in several other organs. Conclusion: Amyloid deposition was caused by amyloidosis secondary to RA. Narrowing of the tumor feeder artery due to amyloidosis may have prevented early enhancement on the CT image. Objective: Whipple's disease is an infectious disease caused by Tropheryma whipplei, an ubiquitous Gram-positive Actinobacteria. The incidence of the disease is less than 1 per 1 milion. We report five new consecutive cases, four males and one female, diagnosed in our clinic from August 2002 to January 2012. Method: Diagnosis was reached with the help of gastroduodenal endoscopy and histopathological examination of the duodenal biopsies, by lymph node biopsy and by electron microscopy.