Objectives: The aim of this study was to analyze the epidemiology of in-hospital injuries including cause, gender, age, hospital level, department, and prognosis. Methods: Data from ”inpatient expenditures by admissions (DD)”, ”registry for contracted medical facilities (HOSB)”, and ”registry for medical personnel (PER)” were linked from the national health insurance research database for 2007 by using SPSS 18.0 software. ”Medical injuries” included ”accidental cut, puncture, perforation or hemorrhage (998.2, E870)”, ”foreign object left in body (998.4, 998.7, E871)”, ”failure of sterile precautions (E872)”, ”failure in dosage (E873)”, ”mechanical failure of instrument or apparatus (E874)”, ”contaminated or infected blood or other fluid, drug or biological substance (E875)”, and ”mismatched blood, fluid, or substance in transfusion (999.6, 999.7, E876)” using ICD-9-CM classifications. Results: There were 1,113 in-hospital injuries (57.98 per 105 inpatients requiring an operation or treatment) in Taiwan in 2007. There were more injuries in females than in males (females: 52.74%, males: 47.26%), and most of them occurred in the 70-74 age group (10.69%). The leading cause of injury was ”accidental cut, puncture, perforation or hemorrhage” (78.80%). Most occurred in medical centers (58.76%), and departments of obstetrics and gynecology had the greatest number (20.31%). Of those cases, 2.52% were discharged against medical advice, 2.07% died, and more than half (56.86%) bad prognosis cases occurred in the medical center. Conclusions: The rate of in-hospital injury was 57.98 per 10^5 patients requiring an operation or treatment, and had been seriously underestimated; however, this research provided evidenced-based data for authorities to implement intervention programs to promote patient safety.