This study investigated the long-term stability of the nine temperament subcategories which underlie the Thomas and Chess temperament clusters. A homogeneous sample of 55 children and parents was recruited (26 remained at the final data collection interval) and parents provided questionnaire responses on their child's temperament at 2, 4, 6, 18, and 39 months; and at 5, 6, and 9 years. All children were first-born from European-American, upper middle class, two-parent families living in a midwestern suburb. The sample was evenly divided between males and females. Chronbach alpha coefficients and bivariate correlation coefficients were calculated to assess overall levels of agreement across the eight assessment periods. The results indicated that there was remarkable stability over time in threshold for stimulation, rhythmicity/predictability, activity level, distractibility, mood, response, and adaptability scores, suggesting that these subcategories reflect enduring characteristics of the child. Chronbach alpha levels ranged from .72 to .87. The two final dimensions, persistence and approach, were stable during the infancy period only. The Chronbach alphas for this period were .69 and .63. (Ten tables delineate findings. Contains 10 references.) (Author/KDFB)