ObjectiveCorrelational studies have frequently linked neuroticism to lower well‐being and poorer social adaptation. In this study, we examined the longitudinal associations of neuroticism with life satisfaction and aspects of social adaptation (i.e., loneliness, number of close friends, and interpersonal trust).MethodCross‐lagged panel models (CLPMs) and random intercepts cross‐lagged panel models (RI‐CLPMs) were used to analyze the prospective associations between variables in a nationally representative adult sample from Germany (N = 5,663 to 11,079 per analysis; 2–4 measurement waves with lags of 4–5 years).ResultsCLPMs indicated that higher neuroticism was related to lower life satisfaction, higher loneliness, fewer friends, and lower interpersonal trust, but not vice versa. At the within‐person level, RI‐CLPMs revealed similar findings with increased neuroticism predicting decreases in life satisfaction, increases in loneliness, and decreases in interpersonal trust. Indices of social adaptation partially mediated the link between neuroticism and life satisfaction at the between‐person but not at the within‐person level. Exploratory multigroup analyses support the generalization of the cross‐lagged effects of neuroticism on life satisfaction and social adaptation across age, gender, and geographical regions (East versus West Germany).ConclusionsThese findings highlight the role of neuroticism in shaping psychosocial outcomes over time.