Background and Objectives: Grip strength is a reliable marker of biological vitality and it typically demonstrates an expected decline in older adults. According to the common-cause hypothesis there is also a significant association between cognitive and physical function in older adults. Some specific cognitive functions have been shown to be associated with grip strength trajectories with most research solely focused on cut-off points or mean cognitive performance. In the present study we examine whether a measure of cognitive dispersion might be more informative. We therefore used an index that quantifies dispersion in cognitive scores across multiple cognitive tests, shown to be associated with detrimental outcomes in older adults. Research Design and Methods: Using repeated grip strength measures from men and women aged 80 and older, free of dementia in the OCTO-Twin study, we estimated ageing-related grip strength trajectories. We examined the association of cognitive dispersion and mean cognitive function with grip strength level and ageing-related rate of change, accounting for known risk factors. Results: Cognitive dispersion was associated with grip strength trajectories in men and the association varied by mean cognitive performance, whereas we found no association in women. Discussion and Implications: Our results provide evidence of a sex-specific vitality association between cognitive dispersion and ageing-related trajectories of grip strength. Our results support the call for integration of sex and gender in health promotion and intervention research.