The principal outcome that is measured in a clinical trial.

Clinical trials typically assess multiple endpoints. The primary endpoint relates specifically to the anticipated clinical impact of an intervention, such as cure or survival, to provide a measure of its efficacy. Secondary endpoints can provide additional information on the effects of an intervention and on mechanisms of action, as well as on possible specific safety issues. Exploratory endpoints cover clinical outcomes likely to be rare or measures that allow hypotheses to be tested.

It is essential that endpoints are selected that provide a reliable assessment of the benefits of an intervention and hence its efficacy. They must be acceptable to all stakeholders, particularly regulatory authorities, which must have confidence in the validity and reliability of endpoints to approve new treatments.