Impulsivity has been identified as a key factor in risk of suicidal behavior in adolescent and adult patients. However, a lack of consensus about the definition of impulsivity has led to difficulty in its measurement. Impulsivity self-report scales exhibit low intercorrelations, are subject to response bias, and incorporate multiple subfactors. Performance tests may be less sensitive to response biases, as well as be more precise measures of dimensions of impulsivity, but each test alone does not provide a comprehensive measure of the trait. Assessing impulsivity in child and adolescent groups presents additional methodological problems, such as an overlap between limited impulse control due to developmental factors and psychopathology. A multiple measures approach to assessing impulsivity is suggested.