Objective: The aim of this article is to study the associations between healthy lifestyle in old age and decline in physical, psychological, cognitive, and social functioning. Method: A population-based sample of 3,107 Dutch men and women aged 55 and 85 years (1992/1993; Longitudinal Aging Study Amsterdam) was used with five 3-yeary follow-up examinations. Lifestyle score, based on smoking status, alcohol consumption, physical activity, and body mass index (BMI), ranged from 0 (unhealthy) to 4 (healthy). Outcomes included gait speed, depressive symptoms, cognitive status, and social contacts. Results: Persons with a healthy lifestyle had a 10.6% slower decline in gait speed (0.04 m/s, 95% confidence interval [CI] = [0.03, 0.05]), 10.8% slower increase in depressive symptoms (–1.07 [–1.70, –0.44]), a 1.8% slower decline in cognitive functioning (0.47 [0.23, 0.70]), and a 4.9% slower decline in social contacts (0.58 [0.01, 1.15]) compared with persons with no or one healthy lifestyle factor. Discussion: A healthy lifestyle benefits physical, psychological, cognitive, and social functioning up to very old age.