AbstractDevelopmental differences in self‐concept, personality integration, flexibility, empathy, and temperament, and the relationship of these variables to maternal behavior, were investigated using three age groups of first‐time mothers. The age groups also were tested for change in self‐concept and personality integration from 1 to 3 days postpartum to 8 months postbirth. The longitudinal study included 60 mothers aged 15–19 years, 138 aged 20–29 years, and 90 aged 30–42 years. Self‐completed instruments were used to measure the personality variables, and an interviewer‐rated instrument measured maternal behavior.Personality integration and flexibility increased significantly and correlated significantly with age indicating that both are developmental constructs. Empathy and temperament traits did not increase with age, although teenage scores were significantly lower in empathy, self‐concept, several temperament traits, and maternal behavior. The two older groups' self‐concept decreased significantly the first eight months of motherhood. In the teenage group personality integration, empathy, activity level, intensity and threshold to stimulus were significantly correlated with maternal behavior. In the 20–29 year‐old group, self‐concept, personality integration, flexibility, rhythmicity, adaptability, intensity and mood quality correlated significantly with maternal behavior. In the older group, self‐concept, flexibility, approach/withdrawal, adaptability, intensity, and mood quality correlated significa