To study the histological changes observed in Giardia positive biopsies obtained from the duodenum.: The number of intraepithelial lymphocytes (IEL), grade of villous atrophy, presence of lymph follicles and number of eosinophils in the lamina propria per HPF were assessed. All giardia positive biopsies diagnosed during period 2005-2009 in 5 pathology units were reevaluated by a group of pathologists. Thirty cases were included. Atrophic villous architecture was seen in 61,2%, increase in number of intraepithelial lymphocytes in 63,3% The occurrence of lymphoid follicles in 43,3%. Villous atrophy was higher than reported by others authors, cases with atrophy showed greater frequency of increase in the number of intraepithelial lymphocytes than cases without atrophy. No cases with lymph follicle showed lack of plasmatic cells, the number of eosinophils was subtly increased.