This paper presents a validation study of a new questionnaire of self-control as an individual trait. The questionnaire has two parallel versions, one based on self-reports (AS-36) and another one based on informant reports (AS-36-3). Each version consists of three subscales, called Inhibition (12 items), Switching (12 items), and Goal Monitoring (12 items). Eight samples of participants (N = 935 altogether) took part in the validation study. Both versions obtained satisfactory indices of internal consistency, assessed with Cronbach’s alpha and split-half coefficients. Selfcontrol assessed with this scale proved to be entirely independent of general intelligence. However, AS-36 and AS-36-3 scores tended to correlate with other self-report measures of trait self control, such as Tangney, Baumeister, and Boone’s (2004) self-control scale. We conclude that AS-36 is a valid and reliable tool, suitable for assessment of self-control in both research and diagnostic settings.