Giardiasis constitutes a very frequent intestinal parasitic infection in our country, with a varied digestive symptomatology. We performed a prospective, transversal study, with the aim to establish the frequency of G. lamblia in digestive symptomatic patients submitted to upper gastrointestinal endoscopy examination trying to relate its isolation with the endoscopic findings. We studied 50 patients; they were submitted to upper endoscopy examination. During the procedure, we aspirated duodenal content and six duodenal biopsies were taken; 8 to 14 hours before endoscopy, they swallowed the Enterotest encapsulated string. The presence of G. lamblia was established by three methods (Enterotest, duodenal content, impront). The day, of the endoscopic examination they resolved a questionnaire of digestive symptoms they had during the last 4 weeks. The endoscopy was informed like normal in 15 patients. (30%). Duodenitis was detected by endoscopy in 9 patients (18%), but neither one of them demonstrated presence of G. lamblia. By the three diagnostic methods, the presence of G. lamblia was demonstrated in 5 patients (19%), without endoscopic duodenitis, being the digestive symptom scores not statistically significant respect to symptomatic patients without G. lamblia. We concluded that the three diagnostic methods used to identify G. lamblia were equally sensitive. No preponderance of digestive symptoms were present in patients with G. lamblia in relation to in our country patients without G. lamblia infection. We recommend to consider duodenal aspiration during endoscopy in order to discard giardiasis.