This article uses the Bradford Hill criteria for assessing causal associations to examine the nature of the relationship between PTSD and alcohol abuse. A series of studies are presented which examine this relationship. A cross-sectional study of 2,501 subjects in a community sample examined the relationship between at-risk drinking and 11 types of traumatic events. The traumatic events associated with at-risk drinking were involvement in life threatening accidents, witnessing severe injury, rape, being the victim of serious physical assault using the CIDI. In a longitudinal study of 469 firefighters exposed to a natural disaster, PTSD was associated with both an increase and decrease in alcohol consumption and PTSD rather than exposure accounted for the changes in drinking behaviour. In three other populations, psychiatric inpatients, motor accident victims and female prisoners, the association between PTSD and alcohol abuse emphasised the clinical and public health importance of this relationship. The available evidence does nevertheless support the causal nature of this relationship. Other risk factors are necessary to predict alcohol abuse following exposure to traumatic events, although exposure to traumatic events can be caused by alcohol abuse.