Few personality traits are as socially relevant as impulsivity, but few self-report measures have been specifically developed for adolescents and children. The aim of the present study was to examine the psychometric properties of the Barratt Impulsiveness Scale version 11 (BIS-11) among a mixed-gender sample of 782 Portuguese youth (M = 15.87 years; SD = 1.72), in a school context. Confirmatory factor analysis revealed the expected 6-factor first-order structure, but the 3-factor second-order factorial structure did not present a good fit. Cross-gender measurement invariance was demonstrated only in terms of weak invariance. Nonetheless, the Portuguese adaptation of the BIS-11 demonstrated some generally acceptable psychometric properties of internal consistency, mean inter-item correlation, convergent validity, discriminant validity, and criterion-related validity of statistically significant associations with conduct disorder symptoms, alcohol abuse, drug use, and unprotected sex. The use of the BIS-11 among the male and female youth population is psychometrically justified, and it can be a useful measure to identify impulsive adolescents who are at considerable risk of personal injury and present a potential source of injury to others.