A population-based sample of Norwegian children aged 18 months (N = 921), 30 months (N = 784), and 50 months (N = 737) was examined with the EAS Temperament Survey (Buss & Plomin, 1984). The factor structure, psychometric properties, and stability estimates of the instrument were assessed. A cross-validation of the temperament factors of Emotionality, Activity, and Shyness show that the covariance structure conforms with the three scales described by Rowe and Plomin (1977) and Boer and Westenberg (1994). When items from the experimental scale of Sociability were included in the analysis, a four-factor solution confirmed the separate usability of this scale as well. The factor structure does not seem to vary substantially with the age of the children. The scores on the four temperament scales show high stability from one time of measurement to the next. Although no strong gender differences were found, there were significant age trends. Emotionality and Shyness increased from 18 to 50 months, while Activity and Sociability decreased. The study confirmed the structure and stability of the EAS over 3 years among young children, providing support for its use with children as young as 18 months.