Non-shared environmental influence (NSE) has been found to account for around 50 percent of anxiety variance, but specific NSE factors have not been identified. Discordant monozygotic (MZ) twins can be used to generate relevant hypotheses because MZ discordance can be caused by NSE, but not by genes or shared environment. Of 1590 MZ pairs teacher rated for anxiety at the age of seven, we selected the most discordant 19 pairs and conducted interviews with them and their mothers. In explaining discordant anxiety, the mothers emphasised negative school experiences, comparisons within the twin relationship, and illness and accidents. During the maternal interviews neonatal life events, parent-child relationships and peer rejection also emerged as potential NSE sources.