Escherichia coli O157:H7 is the most common serotype among verotoxigenic E.coli (VTEC) strains that cause haemolytic uremic syndrome. Although sporadic VTEC cases originating from Turkey and small outbreaks have been reported from our country, VTEC has not been routinely investigated in most of the diagnostic microbiology laboratories in Turkey and studies related to this topic are limited. In this study, the incidence of E.coli O157:H7 in patients who were admitted to Alanya Research and Application Hospital of Baskent University with the complaints of acute gastroenteritis between September 2005 and September 2008, was investigated. Stool samples collected from 1815 diarrheal patients (of them 50.5% were male; 49.3% were ? 5 years old; 10.2% were tourists) were evaluated initially by direct microscopy and then inoculated to hectoen enteric agar, EMB agar, Skirrow agar and cefixime tellurite sorbitol MacConkey (CT-SMC) agar media for cultivation. The sorbitol-negative colonies which were compatible with E.coli according to the conventional methods were tested with E.coli polyvalent and 0157 and H7 monovalent antisera and agglutination positive strains were also investigated for verotoxin production in Vero cell cultures. VTEC RPLA toxin detection kit (Oxoid, UK) was used for further identification of toxin type of verotoxin positive strains. Fecal leukocytes were detected in 41.3% of the samples in direct microscopy, while 27% (173/639) of the samples were also found positive for amoeba antigen, 6% (24/396) for rotavirus antigen, 1.2% (22/1815) for Salmonella spp., 0.6% (11/1815) for Shigella spp., 0.2% (4/1815) for Giardia trophozoites and 0.06% (1/1815) for Campylobacter jejuni. The isolation rate of sorbitol-negative E.coli strains was %0.8 (14/1815), and two of them were identified as E.coli O157:H7 by monovalent antisera, and both of them were determined as verotoxin-producers in cell culture. Verotoxin types of those isolates were found as verotoxin 1 in one strain and verotoxin 1 + verotoxin 2 in the other. The two patients infected with verotoxigenic E.coli O157:H7 were both tourists (one was 7 and the other was 35 years old) and admitted to the emergency room of hospital with complaints of bloody diarrhea. No further investigation directed towards the origin of the pathogen could be performed in the hotels of these patients. These data indicated that VTEC O157:H7 incidence was low (2/1815; 0.1%) in our area during the study period. Thus, routine testing of stool samples for E.coli O157:H7 does not seem to be cost-effective. However, E.coli O157:H7 should necessarily be investigated at least in bloody diarrhea cases since this pathogen has serious morbidity, mortality and complications like haemolytic uremic syndrome, hemorrhagic colitis and also due to its epidemiological significance.