Most cancers are due to modifiable lifestyle and environmental risk factors, and are potentially preventable. No studies have provided a systematic quantitative assessment of the burden of cancer mortality and incidence attributable to known risk factors in China. We calculated the proportions of cancer deaths and new cases attributable to known risk factors in China, based on the prevalence of exposure around 1990 and national data on cancer mortality and incidence for the year 2005. Chronic infection is the main risk factor for cancer in China, accounting for 29.4% of cancer deaths (31.7% in men and 25.3% in women), followed by tobacco smoking (22.6% with 32.7% in men and 5.0% in women), low fruit intake (13.0%), alcohol drinking (4.4%), low vegetable intake (3.6%) and occupational exposures (2.7%). The remaining factors, including environmental agents, physical inactivity, the use of exogenous hormones and reproductive factors are each responsible for <1.0%. Modifiable risk factors explain nearly 60% of cancer deaths in China, with a predominant role of chronic infection and tobacco smoking. Our findings could provide a basis for cancer prevention and control programs aimed at reducing cancer risk in other developing countries.