OBJECTIVE To analyze the causes of medical malpractice in patients with tumor, to determine the medical responsibility, and to recommend the related preventions. METHODS Seventy four medical malpractice cases, which were involved in tumor and collected from 2000 to 2009 in medicolegal expertise center of west China, were analyzed retrospectively. RESULTS The medical malpractice cases in the patients with tumor showed an increasing tendency in recent years. The main causes are missed diagnosis, misdiagnosis, improper chemotherapy and neglect of complications. The causes of medical malpractice were different in the different levels of medical services. The occurrence of medical malpractice in surgery and OB-GYN showed more frequent than the others. CONCLUSION Forensic pathology autopsy is important to resolve medical malpractice of tumor patients by finding out the cause of death and clarifying the medical responsibility. The occurrence of medical malpractice could be reduced by the clinical doctors through improving serve consciousness, obtaining the patients' trust, improving the medical treatment, following related laws and rules, fulfiling duty of medical careness.