Cigarette smoking leads to excess mortality risk. Although it is well known that the risk increases with the number of pack-years of smoking--that is, how much a person smokes, or "habit"--there is apparently no published studies that organize and synthesize the evidence on this topic. This paper provides a meta-analysis of the latest published findings relating to cigarette smoking habit and excess mortality. A combined estimate of the relative risk (RR) of death for smokers, stratified by habit (light, medium, or heavy smoking), compared with non-smokers is provided.