The Twin Interdisciplinary Neuroticism Study (TWINS) is a three-wave study including >800 twin pairs from the northern part of the Netherlands. The aim of the study is to unravel why neuroticism reflects vulnerability to mental disorders. In this study, we focus on possible mechanisms underlying this vulnerability and their genetic and environmental origins. In total, 125 female twin pairs visited our psychophysiological laboratory. From these twin pairs DNA was isolated and both candidate gene and genome-wide genotyping were conducted. Future work includes studies of candidate genes. The study also participates in several meta-genome-wide association study (GWAS) consortia.