Abstract Background The purpose of this study was to evaluate the relationship of lower-limb muscle power with mortality and hospitalization. Methods A total of 1 928 participants from the Toledo Study for Healthy Aging were included. Muscle power was assessed with the 5-repetition sit-to-stand test and participants were classified into different groups of relative power (ie, normalized to body mass) according to sex-specific tertiles and their inability to perform the test. Mean follow-up periods for hospitalization and all-cause mortality were 3.3 and 6.3 years, respectively. Results Compared to the high relative muscle power group, men with low (HR [95% CI] = 2.1 [1.2–3.6]) and women with very low and low (HR [95% CI] = 4.7 [3.0–7.4] and 1.8 [1.2–2.7]) relative power had an increased age-adjusted risk of hospitalization. After adjusting for several covariates (age, physical activity, body mass index education, depression, comorbidities, disability, and handgrip strength), these effects were attenuated (men and women with very low relative power: HR [95% CI] = 1.6 [0.9–2.9] and 2.8 [1.6–4.9]). The very low relative muscle power group had also an increased all-cause mortality risk (age-adjusted) in both men and women (HR [95% CI] = 2.3 [1.4–3.9] and 2.9 [1.6–5.3]). After adjusting for all the covariates, a significantly increased mortality risk was observed only in men (HR [95% CI] = 2.1 [1.1–3.8]; women HR [95% CI] = 1.6 [0.8–3.2]), with very low levels of relative power. Conclusions Relative muscle power was independently and negatively associated with mortality and hospitalization in older adults. An augmented all-cause mortality risk was noted in the lowest group of relative muscle power.