The ability of prebiopsy coagulation assays to predict mild postbiopsy bleeding was evaluated in renal transplant patients undergoing renal allograft biopsy (N = 120). The coagulation assays studied included the bleeding time, prothrombin time, partial thromboplastin time, platelet count, and thromboelastograph (TEG). Coagulation results were defined as abnormal if they fell outside the established normal reference range. Bleeding was defined as a drop in the hematocrit equal to or more than 4 points 6 h after the procedure or ultrasound evidence of a new perirenal hematoma. Overall, 21% of patients showed evidence of mild bleeding. Of those who bled, 78% had normal results on all coagulation tests, indicating that most mild bleeding was not associated with coagulation abnormalities. Of the assays tested, only abnormal TEG:angle (P < 0.01) and TEG:k (P < 0.04) values were associated with an increased risk of bleeding. Bleeding times were not predictive of an increased risk of postbiopsy bleeding; five patients had abnormal bleeding times ranging from 10 to 20 min of whom only one bled. All prothrombin time, partial thromboplastin time, and platelet count abnormalities were mild (e.g., no prothrombin times longer than 15 s, no platelet counts below 129,000/microL); none of these assays predicted postbiopsy bleeding. Other clinical characteristics, including patient age, sex, serum creatinine, blood pressure (if less than 160/90 mm Hg), number of biopsy passes, or renal pathology, did not appear to influence bleeding after biopsy. It was concluded that most bleeding after transplant renal biopsy was not associated with coagulation abnormalities and that the TEG was the best assay for detecting mild coagulation abnormalities associated with an increased risk of bleeding.