Background and aims: Aging people show a deterioration in a variety of functions. Knowledge about factors that may delay this deterioration is crucial for identifying causal pathways and potential intervention strategies. Physical fitness has been proposed to be such a factor, but longitudinal studies have been scarce. This study determined the influence of physical functioning on cognitive performance both cross-sectionally and longitudinally over a period of six years in a healthy adult population sample. Methods: Data were used from a longitudinal study involving 703 participants in the 24-86 year age range, as part of the Maastricht Aging Study (MAAS). Physical functioning was measured with the SF-36 health questionnaire. Participants were tested using cognitive tests of verbal memory, executive functioning, reaction time and information processing speed, both at baseline and at a six-year follow-up examination. Results: At baseline, physical functioning was positively associated with scores on tests of executive functioning. Participants with an increase in physical functioning were less likely to experience cognitive decline during the six years of follow-up. After correction for age, sex, educational level, baseline physical functioning and cognitive performance, physical functioning at follow-up was still positively associated with scores on tests for executive functioning (Stroop-interference) and information processing speed (Letter-Digit Substitution Test). The observed effects remained unchanged when six participants who developed a neurodegenerative disorder during the course of the study were excluded. Conclusion: Physical functioning has a significant positive effect on cognitive performance after six years in normally aging adults.