Lithium is a common treatment for bipolar disorder, but only some individuals exhibit a favorable response. To identify genetic factors influencing lithium response, the Taiwan Bipolar Consortium performed a genome-wide association study of individuals treated for bipolar I disorder (N. Engl. J. Med. 370, 119–128, 2014). In the discovery phase, the authors studied 294 individuals who had shown good adherence to lithium treatment for bipolar disorder over at least a 2-year period. By testing common variants for association with treatment response using a standardized cutoff, they identified a cluster of SNPs at 3p24.1 that reached genome-wide significance. They subsequently replicated association of the two lead SNPs at 3p24.1 with lithium response in two additional cohorts. In a combined analysis of 394 subjects, the response allele at rs17026688 yielded an odds ratio of 82.2 and a positive predictive value of 83%. Through further resequencing of the region, the authors identified a 1-bp deletion in intron 8 of GADL1 that is in complete linkage disequilibrium with rs17026688 and that may influence GADL1 splicing. If confirmed in larger cohorts, these markers will be useful for identifying the individuals most likely to benefit from lithium treatment.