Little is known about the role of diabetes as a risk factor for cardiovascular disease in the Chinese population. Below the threshold for diabetes, substantial uncertainty exists about the association of blood glucose levels with cardiovascular disease in Chinese populations and more generally.Data from the China Kadoorie Biobank of 0.5 million middle‐aged Chinese adults demonstrated a doubling of the odds of prevalent ischaemic heart disease and stroke/transient ischaemic attack among people with self‐reported diabetes. Among people without prior diabetes, blood glucose levels were positively associated with prevalent cardiovascular disease.A comprehensive understanding of the role of both blood glucose levels and diabetes in cardiovascular disease risk is fundamental to effective disease prevention and control.