Abstract: This paper reports 168 cases of multiple primary malignant tumors cured in Zhejiang Tumor Hospital within 15 years, these cases account for 0. 66 0 o of total malignant tumors cases in the same period, and the rate was lower than the results of outcountry's reports. The cases that the second primary malignancies occured within 3 years account for 52. 11 0 o，it is the period that there currancy and metastasis appear more frequently after the treatments of the primary cancer, so these cases should be critically identified in the follew-up, for the treatments and the prognosis of these two different situations are principlly different. The etiopathology of the multiple primary malignancy, including individual sensitives，immuno-deficient，radiotherapy, carcinogenic factor sand inherent factors，and so on，are discussed in this paper.