An outbreak of highly pathogenic avian influenza A (H5N1) that had previously been detected throughout Asia, with major economic and health repercussions, extended to eastern Turkey in late December 2005 and early January 2006. We documented the epidemiologic, clinical, and radiologic features of all cases of confirmed H5N1 virus infection in patients who were admitted to Yuzuncu Yil University Hospital in Van, Turkey, between December 31, 2005, and January 10, 2006. H5N1 virus infection was diagnosed in eight patients. The patients were 5 to 15 years of age, and all eight had a history of close contact with diseased or dead chickens. The mean (+/-SD) time between exposure and the onset of illness was 5.0+/-1.3 days. All the patients had fever, and seven had clinical and radiologic evidence of pneumonia at presentation; four patients died. Results of enzyme-linked immunosorbent assay and rapid influenza tests were negative in all patients, and the diagnosis was made by means of a polymerase-chain-reaction assay. H5N1, which causes a spectrum of illnesses in humans, including severe and fatal respiratory disease, can be difficult to diagnose. Copyright 2006 Massachusetts Medical Society.