The association between a polymorphism in the promoter area of the serotonin transporter (17q11.1-q12) with impulsivity and history of aggressive behavior was studied in a Spanish general hospital. Subjects comprised 216 suicide attempters (152 women and 64 men) and 223 control blood donors (124 women and 99 men). They were classified as S individuals (s/s or s/l) with low expression of the serotonin transporter, and L individuals (l/l) with high expression. The genotype was not associated with high levels of impulsivity (measured with the Barratt Impulsiveness Scale) or history of aggressive behavior (measured with the Brown-Goodwin scale). This lack of association did not appear to be explained by lack of statistical power. High scores on the Barratt Impulsiveness Scale (BIS) and the Brown-Goodwin Aggressive Behavior Scale were associated with being an attempter, male gender and borderline personality disorder. While our Spanish suicide attempters and published US suicide attempters have similar BIS scores, our Spanish suicide attempters have significantly lower aggressive behavior scores. If cross-cultural differences in aggressive behavior scores are definitively established, country norms for aggressive behavior scales will need to be developed to compare genetic studies in different countries.