Coffee and tea are among the most widely consumed beverages in adults worldwide [1, 2]. Coffee consumption is very popular and still increasing, with the highest per capita consumption in Scandinavian countries in 2013 [3]. Tea (black or green) is worldwide the most commonly consumed beverage after water, with high per capita consumption observed in Turkey, Iran, and United Kingdom [3]. There is a long-standing interest in the health effects of coffee and tea. Epidemiological studies have been conducted on coffee or tea intake and disease incidence (e.g. cancer, CVD, diabetes) and mortality. A recent metaanalysis on coffee and mortality in 31 cohort studies [4] showed decreased overall and cardiovascular disease (CVD) mortality for coffee consumption of up to 4 cups/day. Two recent large cohort studies also showed that coffee consumption was associated with reduced risk of death (overall and from various causes) in the European Prospective Investigation into Cancer (EPIC) [5] and among African Americans, Japanese Americans, Latinos and whites in the Multiethnic Cohort (MEC) [6]. For tea, a recent meta-analysis using 18 cohort studies found that black tea consumption was significantly inversely associated with overall and cancer mortality, while green tea consumption was significantly inversely associated with overall and CVD mortality [7]. Only in a limited number of the previous cohort studies on mortality, analyses for coffee and tea intake were mutually adjusted. While coffee and tea are both drunk in most countries, usually one predominates because of economic (e.g., trade and income), marketing, cultural and ethnic reasons [8]. Many people can choose between coffee and tea, and drink these in varying ratios depending on taste preference, lifestyle, socio-economic factors, genetics and health, but in very few mortality studies associations with coffee and tea have been investigated simultaneously, and no studies have been conducted on possible effects associated with substituting one beverage for the other. This study first evaluated the mutually-adjusted associations between coffee and tea intake with overall and cause-specific mortality in men and women, and then focused on substituting one beverage for the other, as well as on the combined effects of coffee and tea.