AIM:To investigate endoscopic and histopathological findings in the duodenum of patients with Strongyloides stercoralis(S.stercoralis)hyperinfection. METHODS:Over a period of 23 years(1984-2006),we investigated 25 patients withS.stercoralis hyperinfection who had had an esophagogastroduodenoscopy before undergoing treatment for strongyloidiasis.The clinical and endoscopic findings were analyzed retrospectively. RESULTS:Twenty-four(96%)of the patients investigated were under immunocompromised condition which was mainly due to a human T lymphotropic virus type 1(HTLV-1)infection.The abnormal endoscopic findings,mainly edematous mucosa,white villi and erythematous mucosa,were observed in 23(92%) patients.The degree of duodenitis including villous atrophy/destruction and inflammatory cell infiltration corresponded to the severity of the endoscopic findings. The histopathologic yield for identifying larvae was 71.4% by duodenal biopsy.The endoscopic findings of duodenitis were more severe in patients whose biopsies were positive for larvae than those whose biopsies were negative(Endoscopic severity score:4.86±2.47vs 2.71 ±1.38,P<0.05). CONCLUSION:Our study clearly demonstrates that,in addition to stool analysis,endoscopic observation and biopsies are very important.We also emphasize that S.stercoralis and HTLV-1 infections should be ruled out before immunosuppressive therapy is administered in endemic regions. AIM: To investigate endoscopic and histopathological findings in the duodenum of patients with Strongyloides stercoralis (S. stercoralis) hyperinfection. METHODS: Over a period of 23 years (1984-2006), we investigated 25 patients with S.stercoralis hyperinfection who had had an esophagogastroduodenoscopy before undergoing treatment for strongyloidiasis.The clinical and endoscopic findings were analyzed retrospectively. RESULTS: Twenty-four (96%) of the patients investigated were under immunocompromised condition which was mainly due to a human T lymphotropic virus type 1 (HTLV-1) infection The abnormal endoscopic findings, mainly edematous mucosa, white villi and erythematous mucosa, were observed in 23 (92%) patients. The degree of duodenitis including villous atrophy / destruction and inflammatory cell infiltration corresponded to the severity of the endoscopic findings. The histopathologic Yield for identifying larvae was 71.4% by duodenal biopsy.The endoscopic findings of duodenitis were more severe i n patients whose biopsies were positive for larvae than those whose partial biopsies were negative (Endoscopic severity score: 4.86 ± 2.47 vs 2.71 ± 1.38, P <0.05). CONCLUSION: Our study clearly demonstrates that, in addition to stool analysis, endoscopic observation and biopsies are very important. We also emphasize that S. stercoralis and HTLV-1 infections should be ruled out before immunosuppressive therapy is administered in endemic regions.