The incidence of Meckel's diverticulum(MD) in general population has been assessed as 2 percent. The major complications of MD are bleeding, perforation, and intestinal obstruction. In spite that the complication rate of Meckel's diverticulum is relatively high(about 4.2% during a lifetime), the preoperative diagnostic rate of complicated MD is very low. Authors investigated the clinical characteristics of complicated MD to improve the diagnostic rate. 16 patients with complicated Meckel's diverticulum who were operated upon at the Department of Pediatric Surgery, Seoul National University Children's Hospital from June 1985 to December 1993 were reviewed. Among the 16 patients with complicated MD, 12 patients(75%) were under 2 year-old and male were predominant(88%). The most common complication was bleeding patients with bleeding MD (8 cases) were diagnosed preoperatively as MD. 8 patients with other complications(perforation : 4 cases, obstruction: 4 cases) could not be suspected as complicated MD except one patient who had previous history of melena. These patients were diagnosed after exploratory laparotomy under the various impression other than MD. Among 12 patients with ulcer related complications such as bleeding and perforation, heterotopic gastric mucosa was found in 11 patients. In conclusion, in any children with unexplained acute abdomen, especially under 2 years old, complicated MD must be included in differential diagnosis. In children with obscure lower gastrointestinal bleeding,^99m Tc-pertechnetate scintigraphy is a useful diagnostic tool to rule out bleeding MD.