Upper gastrointestinal (UGI) bleeding remains a great medical problem despite the improvement in both diagnostic and therapeutic management. We retrospectively analyzed 560 cases (male 429 cases, female 131 cases, mean age 45.8 +/- 23.1 years) of acute UGI bleeding within one year from January to December 1980, and 1872 cases (male 1395 cases, female 477 cases, mean age 48.7 +/- 27.5 years) within one year from January to December 1989, in order to define the changing pattern of etiology in the past 10 years. The major cause of bleeding was duodenal ulcer bleeding, which occurred at the age of 20-40 years. The incidence significantly decreased (57.8% in 1980 VS. 46.3% in 1989, P < 0.001). The second common cause was gastric ulcer (11.1% VS. 13.5%), which occurred mainly at the age of 50-70 years. The third was esophageal varices bleeding with a significantly increased incidence (6.6% VS. 11.4%, P < 0.001), which occurred mainly at the age of 40-60 years. The other less common causes included gastric cancer (5.9% VS. 5.8%), which occurred mainly at the age of 50-70 years, gastric erosion (5.2% VS. 6.1%), Mallory Weiss tear (2.1% VS. 3.1%), esophagitis (1.9% VS. 2.9%), Dieulafoy's ulcer (1.6% VS. 2.7%), vascular lesion (1.6% VS. 2.6%), and non-diagnostic cases (6.2% VS. 5.6%). The ratio of male to female for each etiology of UGI bleeding was about 3 to 1 in both 1980 and 1989.(ABSTRACT TRUNCATED AT 250 WORDS)