This study examined the effect of health worry (i.e., cognitive aspect of anxiety resulting from concern for health) on walking difficulty in a nationally representative sample (N = 7,527) of older adults (M age = 76.83 years). The study further tested whether physical activity mediates the effect of health worry on walking difficulty in a 6-year follow-up design. Results of a mediation analysis using structural equation modeling showed that people with a high degree of health worry engaged in less physical activity ([beta] = -0.24, p less than 0.001), and people who participated in less physical activity were more likely to report walking difficulty at the 6-year follow-up ([beta] = -0.22, p less than 0.001). There was a significant indirect effect from health worry to walking difficulty through physical activity ([beta] = 0.05, p less than 0.001), controlling for demographic, psychosocial, and health related factors. Results suggested that inducing threat and worry may not be effective for physical activity promotion in the older population. More promising coping and regulation strategies are discussed. (Contains 3 tables, 1 figure and 2 notes.)