The aim of this study was to investigate the predictive factors which contribute to diagnosis of hantavirus infection. One hundred patients from rural areas hospitalized with a preliminary diagnosis of hantavirus infection from different hospitals in Turkey were investigated. Hantavirus infection was confirmed in 20 patients (Group 1) using immunofluorescence and immunoblot assays at the Refik Saydam National Public Health Agency. Hantaviruses were not detected in the serum of the remaining 80 patients, other infectious and non-infectious diseases being diagnosed in this group (Group 2). Patients' demographic characteristics and clinical and laboratory data on admission were examined and compared between the two groups. Fever, proteinuria, hematuria, lethargy-weakness, and nausea-vomiting were the most frequent symptoms and findings in Group 1, seen in almost all patients. Proteinuria, hematuria, muscle pain, diarrhea/abdominal pain, hypotension, shock, and sweating were observed at significantly higher levels in Group 1 compared to Group 2. Serum urea, creatinine, uric acid, lactate dehydrogenase (LDH), aspartate transaminase (AST), alkaline phosphatase (ALP), and C-reactive protein (CRP) were significantly higher, but serum platelet counts were lower in Group 1 patients. Area beneath the receiver operating characteristics (ROC) curve analysis was used to calculate the discriminative ability of various laboratory values to identify patients with hantavirus infection. This analysis revealed that, serum CRP had a 100% negative predictive value, whilst, platelet, and creatinine had 75% and 70% positive predictive values for the diagnosis of hantavirus infection. In summary, laboratory markers used in clinical practice are of great importance predicting hantavirus infections. J. Med. Virol. 84:17901796, 2012. (c) 2012 Wiley Periodicals, Inc.