Three questionnaire studies are reported in which sets of items traditionally used to measure impulsiveness were intercorrelated were correlated with measures of the major personality dimensions E (extraversion), N (neuroticism) and P (psychoticism), and also with the L (lie; dissimulation) scale. It It was found that impulsiveness in the broad sense (ImpB) breaks down into four factors (narrow impusliveness or ImpN, risk-taking, non-planning and liveliness) which are replicable from sample to sample and from males to females. These factors are positively correlated with each other and also with sociability to varying degrees. ImpB correlates quite well with extraversion, but even better with psychoticism; ImpN correlates positively with N and P, suggesting that this trait is somewhat pathological. It is suggested that the distinction between ImpB and ImpN is crucial for the discussion of the nature and measurement of extraversion and also for future experimental work on the causal background and experimental testing of impulsive behaviour patterns.