This presentation provides an overview of cohort studies and relative risk. The learning objectives are to be able to: Define a cohort study and the steps for the study; Understand the populations in a cohort study; Understand timing in a cohort study and the difference between retrospective, prospective and ambi-directional cohort studies; Understand the selection of the cohort population and the collection of exposure and outcome data; Understand the sources of bias in a cohort study; Understand the calculation and interpretation of the relative risk; and, Understand use of the new-castle Ottawa quality assessment score for cohort studies.