The etiological factors, clinical characteristics, diagnosis, treatment strategies, and prognosis of multiple primary malignant neoplasms (MPMNs) were investigated in order to improve its diagnosis and therapy. Clinical data of 170 patients with MPMN who were admitted to the Oncology Department of the First Affiliated Hospital of Anhui Medical University from January 2004 to April 2010 were collected and analyzed retrospectively. The overall incidence of MPMNs was 2.25%. There were 167 cases with duplex primary cancers, 2 cases with triple primary cancers, 1 case with quadruple primary cancer, 46 synchronous MPMNs (SMPMNs), and 124 metachronous MPMNs (MMPMNs). There were 344 malignant neoplasms in the 170 MPMN patients, of which 161 were in the alimentary system, 48 in the respiratory system, 63 in mammary glands, 30 in the genital system, 7 in the urinary system, 23 in the head and neck, and the other 12 were in the brain, hematological system, and soft tissue. There were 22 cases of bilateral primary breast cancer and 41 cases of digestive MPMN. With a median survival time of 24 months, the 1-, 3-, and 5-year cumulative survival rates in the 170 patients were 68.8, 39.1, and 25.2%, respectively. The most common locations of MPMN were the alimentary system, mammary gland, and respiratory system. MPMN usually occurred in distinct organs of identical systems, conjugate organs, or identical organs. The survival rate of SMPMN was similar to that of MMPMN. There were differences in principles of treatment and diagnosis between MPMN and metastasis or recurrent cancers.