Background Mild parkinsonian signs (MPS), highly prevalent in older adults, predict disability. It is unknown whether energy decline, a predictor of mobility disability, is also associated with MPS. We hypothesized that those with MPS had greater decline in self-reported energy level (SEL) than those without MPS, and that SEL decline and MPS share neural substrates. Method Using data from the Health, Aging and Body Composition Study, we analyzed 293 Parkinson’s disease-free participants (83 ± 3 years old, 39% Black, 58% women) with neuroimaging data, MPS evaluation by Unified Parkinson Disease Rating Scale in 2006–2008, and ≥3 measures of SEL since 1999–2000. Individual SEL slopes were computed via linear mixed models. Associations of SEL slopes with MPS were tested using logistic regression models. Associations of SEL slope with volume of striatum, sensorimotor, and cognitive regions were examined using linear regression models adjusted for normalized total gray matter volume. Models were adjusted for baseline SEL, mobility, demographics, and comorbidities. Results Compared to those without MPS (n = 165), those with MPS (n = 128) had 37% greater SEL decline in the prior 8 years (p = .001). Greater SEL decline was associated with smaller right striatal volume (adjusted standardized β = 0.126, p = .029). SEL decline was not associated with volumes in other regions. The association of SEL decline with MPS remained similar after adjustment for right striatal volume (adjusted odds ratio = 2.03, 95% CI: 1.16–3.54). Conclusion SEL decline may be faster in those with MPS. Striatal atrophy may be important for declining energy but does not explain the association with MPS.