<i>Aim:</i> To evaluate results of coagulation tests and serum sodium levels during the early postoperative period in patients undergoing transurethral resection of the prostate. <i>Patients and Methods:</i> In a prospective study, blood coagulation tests were performed and serum sodium levels measured in 27 patients before and at the end of transurethral resection of the prostate and 24 h later. The causes of the changes in coagulation test results were also investigated. <i>Results:</i> There were significant decreases in the platelet counts (p < 0.001) and fibrinogen (p < 0.001), hemoglobin (p < 0.05), and sodium (p < 0.0001) concentrations at the end of the operation. The prothrombin time was prolonged (p < 0.01). The activated partial thromboplastin time did not change. There was a statistically significant correlation between the changes in prothrombin time and fibrinogen concentration and the amount of irrigating solution used during the operation and the difference between the volume given and collected as irrigation. Coagulation test results, hemoglobin concentration, and serum sodium level returned to normal values 24 h after the operation. <i>Conclusion:</i> Our results show that there was a transient change in platelet count, prothrombin time, and fibrinogen and serum sodium concentrations during the early postoperative period which can be explained on the basis of dilution of the blood.