Stability of temperament over successive ages in the first 2 years was evaluated for 109 full-term and 81 preterm infants who were assessed at 6, 9, 12, 18, and 24 months of age. At each age subjects were engaged in a series of age-appropriate vignettes in the laboratory; experimenters used a structured sequence of activities. Composite ratings were made of emotional tone, attentiveness, activity, and orientation to staff. Correlations computed over ages indicated, for full term infants, significant stability across ages. Significant stability was also demonstrated for two separate measures of period-to-period variability at each age: for emotional tone-variability, beginning at 6 to 9 months; for activity-variability, beginning at 12 to 18 months. The same pattern of stability was not observed for the preterm infants. Stability across ages generally was not observed until the later months of infancy or toddlerhood. Occasionally stability was sporadic, and occasionally it was not observed by 18 to 24 months. Findings indicated that, for full-term infants, stable aspects of temperament were apparent during the first year of life. In contrast, individual differences were not as clearly defined for preterm infants until later infancy or toddlerhood. Results suggested that prematurity depresses longitudinal stability of temperament during the first year of life. (Author/RH)