To investigate the causes of gastrointestinal bleeding (GIB) and its impact on patient and graft survival after orthotopic liver transplantation (OLTx), the first 1000 consecutive OLTx using tacrolimus were studied. Our patient population consisted of 834 adults. The bleeding episodes of patients with GIB (n=74) were analyzed, and patients without GIB (n=760) were used as controls. The mean age, gender, and United Network for Organ Sharing status were similar in both groups. Endoscopy was done in 73 patients with GIB and yielded a diagnosis in 60 patients (82.2%): 39 with a single, and 21 with multiple GIB episodes. In the remaining 13 patients (17.8%), the bleeding source was not identified. Of 92 GIB episodes with endoscopic diagnoses, ulcers (n=25) were the most common cause of bleeding, followed by enteritis (n=24), portal hypertensive lesions (n=15), Roux-en-Y bleeds, and other miscellaneous events (n=28). The majority (73%) of the GIB episodes occurred during the first postoperative trimester. The patient and graft survival rates were statistically lower in the GIB group compared with the control group. The adjusted relative risk of mortality and graft failure was increased by bleeding. In summary, the cumulative incidence of GIB was 8.9%. Endoscopy identified the source of GIB in most cases. Ulcers were the most common cause of GIB after OLTx. The onset of GIB after OLTx was an indicator of decreased patient and graft survival.