Bipolar patients present increased levels of impulsivity even during remission periods. It is known that this dimensional trait negatively impacts on the course of illness and worsens their prognosis and outcome. Evidence from both basic and clinical researches supports that Lithium (Li) may decrease impulsivity. Owing to the fact that Li inhibits both glycogen synthetase kinase-3 (GSK3) isoenzimes, our aim was to analyze the potential impact of genetic variants located at the GSK3 α and β genes on impulsivity levels in a bipolar sample. Our sample consisted of 199 unrelated Caucasian bipolar outpatients who were recruited from the Bipolar Disorder Unit of the Hospital Clinic of Barcelona and from primary care settings from Oviedo. Four polymorphisms at the GSK3 α and β genes were genotyped in order to analyze the impact of genetic variability on impulsivity as measured by the BIS-11 scale. Single SNP analysis showed that patients carrying T and G alleles at the rs1732170-GSK3β and the rs334558-GSK3β, respectively, presented increased levels of attentional impulsivity compared to non-carriers. These results were also confirmed by haplotype analysis. Our results suggest that genetic variability at GSK3β gene is associated to increased impulsivity in bipolar patients.