Authors report the results of four meta-analyses of studies that examined the association between methylenetetrahydrofolate reductase (MTHFR) C677T and A1298C polymorphisms and head and neck cancer (nine studies, 2076 cases and 4834 controls for C677T; four studies, 1439 cases and 3941 controls for A1298C), and lung cancer (ten studies, 5274 cases and 7435 controls for C677T; seven studies, 5098 cases and 6243 controls for A1298C).