To evaluate the gastrointestinal tolerability of nonsteroidal antiinflammatory drugs (NSAIDs) in osteoarthritis patients in Japan, a systematic review of Japanese randomized controlled trials was performed. This study consisted of double-blind, randomized, controlled clinical trials with 4-week NSAID treatment of osteoarthritis patients in Japan. The analysis included 4725 patients from 25 trials. On average the cumulative incidences of patients who had experienced any adverse reaction and any adverse digestive reaction were 14.3% [95% confidence interval (CI) 13.3%-15.3%] and 10.4% (95% CI 9.4%-11.4%), respectively. The cumulative incidence for the upper gastrointestinal (GI) symptoms such as abdominal pain, nausea/vomiting, and dyspepsia was estimated to be approximately 10.9%. When the risk of upper GI symptoms was compared between males and females, the summary odds ratio was 1.71 (95% CI 1.11-2.65). Comparing the risk of upper GI symptoms between patients 59 years of age and younger and those 60+ years old, the summary odds ratio was 1.07 (95% CI 0.75-1.52). Despite the incidence of adverse reactions varying across the drugs being used, there was an obvious increased risk of GI symptoms.