Variation in the promotor region of the serotonin transporter gene (5-HTTLPR) is a promising candidate for better understanding individual heterogeneity in subjective well-being or happiness, as measured by life satisfaction. This functional polymorphism has previously been associated with mental health and selective processing of positive and negative emotional stimuli. A case-control association study on a representative sample of Americans (N=2574) finds that individuals with the transcriptionally more efficient version of the serotonin transporter gene, report significantly higher levels of life satisfaction (P=0.01). This new finding may help explain the important genetic component of the individual baseline levels of happiness.