Abstract: Objective　The study was conducted to provide an assessment of under-reporting of birth, death, infectious diseases and chronic diseases in Zhejiang based on the surveillance data in 2007. Methods　Based on the Capture-Signed-Capture principle, a multi-stage randomized cluster sample of 93 599 families were selected from 30 public health surveillance areas to analyze the under-reporting of infectious diseases of the past year and birth and major chronic diseases in the past three years. Results　A total of 93 599 families from 30 counties (districts) consisting of 280 164 residents were surveyed in the study, including 100 658 urban residents (35.93%) and 179 505 rural residents( 64.07%). The sex ratio was 1.03∶1 which was consistent with the ratio of the general population. The number of birth was 5179， 460 were under-reported (8.88%), the under-reporting rate of birth was 19.04% in urban areas and 4.31% in rural areas. The number of death was 3447, 183 were under-reported (5.31%); the under-reporting rate of death was 8.18% in urban areas and 4.43% in rural areas. A total of 403 cases of infectious disease were found, 37 were under-reported (9.18%), and the under-diagnosing rate was 9.44%. In urban areas, the under-reporting rate of infectious diseases was 6.67% and under-diagnosing rate was 0.94%, in rural areas, the two rates were 10.07% and 12.09% respectively. A total of 3077 cases of chronic disease were found, 1003 cases were under-reported. The overall under-reporting rate of four major chronic diseases was 32.60% (23.95% for malignant tumor, 45.97% for diabetes, 39.01% for coronary artery diseases and 29.69% for apoplexy). Conclusion　Statistical results revealed that the under-reporting rates of birth and death were higher in urban areas and in rural areas in Zhejiang, whereas the under-reporting rates of infectious diseases were of no statistical difference. Higher under-reporting rates of four chronic diseases were mostly seen in the large-scale hospitals at provincial and municipal levels.