Objectives: To determine whether alendronate sodium treatment is associated with upper gastrointestinal (GI) tract adverse experiences (AEs) - particularly those of the stomach, duodenum, or esophagus - in the Fracture Intervention Trial, and to assess the relationship between alendronate use and upper GI tract events among women at increased risk for these outcomes. Design: Randomized, double-blind, placebo-controlled trial with a mean follow-up of 3.8 years. Women were initially randomized to receive alendronate sodium, 5 mg/d, or placebo. After 2 years, the alendronate sodium dose was increased to 10 mg/d. Participants: A total of 6459 women aged 54 to 81 years recruited from 11 US clinical centers. All participants had low hip bone mineral density. Women with major upper GI tract disease (recent ulcers, upper GI tract bleeding, or use of daily medication for dyspepsia) were excluded. Regular nonsteroidal anti-inflammatory drug users were not excluded. Measurements: Self-reported upper GI tract AEs were ascertained by interview every 3 months. Serious upper GI tract AEs were confirmed and classified by review of hospital records and endoscopy reports, if available. Upper GI tract AEs were further analyzed in 2 specified groups - gastroduodenal and esophageal - to examine events that might be related to upper GI tract mucosal irritation. Gastric and duodenal perforations, ulcers, and bleeding events were combined for analysis of these clinically important outcomes. Results: The overall incidence of upper GI tract events was similar in the alendronate and placebo groups (47.5% vs 46.2%; relative risk [RR], 1.02; 95% confidence interval [CI], 0.95-1.10). The incidence of gastroduodenal perforations, ulcers, and bleeding events was 1.6% in the alendronate group and 1.9% in the placebo group (RR, 0.86, 95% CI, 0.59- 1.24). The incidence of nonspecific upper GI tract conditions, such as abdominal pain, dyspepsia, nausea, and vomiting, was also similar in the 2 groups. Esophageal events occurred in 10.0% and 9.4% of patients in the alendronate and placebo groups, respectively (RR, 1.06; 95% CI, 0.91-1.24). Esophagitis not reported as reflux was more common in the alendronate group (0.7%) than in the placebo group (0.4%), but not significantly so (RR, 1.71; 95% CI, 0.90-3.39). Alendronate use was not associated with a significant increase in upper GI tract events among women at increased risk for these events (those aged ≥75 years with previous upper GI tract disease or using nonsteroidal anti-inflammatory drugs). Conclusion: In these older women, upper GI tract complaints, particularly dyspepsia and abdominal pain, were common, but alendronate treatment was not associated with an increased incidence of upper GI tract events, even in high-risk subgroups.