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Objective: The purpose of this study was to define the 'sensitivity' and 'specifity' of ESR and CRP values for the diagnosis of periprosthetic joint infection by comparing them with positive and negative microbiological cultures. Materials and Methods: We retrospectively analysed the data of 80 patients with the diagnosis of infected primary hip or knee arthroplasty, and noted ESR and CRP levelsas well as intraoperative microbiological culture results. ESR rates over 30 mm/h and CRP rates over 10 mg/dl were defined as positive test, and rates under these values defined as negative test. Culture results were also divided as negative (sterile) and positive.Results: According to our results, CRP had 98% sensitivity (ranges, 88% to 99 %) and 0 % specificity (ranges, 0 % to 15%) for the diagnosis periprosthetic infection; ESR had 98% sensitivity (ranges, 88% to 99 %) and 7 % specificity (ranges, 1% to 25 %) for the diagnosis periprosthetic infection. Conclusion: CRP and ESR tests are valuable and sensitive tests for the diagnosis of periprosthetic infection. On the other hand, orthopedic surgeons must be aware of false positive results of these tests and further investigation should be added for the definite diagnosis if needed.