This study examined whether cardiorespiratory fitness influences cognitive ageing and whether this influence is domain specific. A cross-sectional design comprising 25 young (18-30 years), 25 young-old (65-74 years), 25 middle-old (75-84 years) and 25 old-old adults (85-92 years) compared the relationship between cardiorespiratory fitness (VO(2max)) and measures of processing resources (attention, working memory, speed) and higher-order cognitive functions (executive function, memory). Fitness was a strong predictor of cognition and accounted for more variance in processing resources than in higher-order functions. This suggests that cardiorespiratory fitness may have a selective protective effect against age-associated cognitive decline.