Abstract: Diabetes and cancer are two major chronic diseases with tremendous impact on human health worldwide. Clinical and basic studies demonstrate that diabetes can promote carcinogenesis and tumor progression. High insulin and high insulin-like growth factor are considered to be the major risk factors for cancer. Chronic inflammation and aberrant metabolism also participate in cancer development. It is noteworthy that therapies used for treatment of diabetes may increase or decrease the risk of cancer. Revealing the mechanisms that connect diabetes to cancer will be crucial for prevention and treatment of diabetes-related cancers.