Moderate consumers of alcohol have lower mortality than either nondrinkers or heavy drinkers. This systematic review aimed to quantify the level of alcohol consumption (termed the nadir) at which the lowest mortality occurs. Twenty cohort studies reported analyses of all-cause mortality for at least three categories of alcohol consumption, giving a total of 60,224 deaths among men and 74,824 deaths among women. The nadir in each study was estimated for men and women separately in units per week, where 1 unit is 9 g of alcohol. The estimated nadirs varied substantially between countries. Combined nadirs were estimated for U.S. men (overall nadir 7.7 units per week, 95% confidence interval [CI] 6.4-9.1), U.K. men (12.9 units per week, 95% CI 10.8-15.1), and U.S. women (2.9 units per week, 95% CI 2.0-4.0). The nadirs were not found to be increased in studies of older persons and apply for ages 50 to 80 years.