Background <p>The present study examined the associations between malnutrition and physical function, sarcopenia, and frailty in older adults.</p> Methods <p>This was a prospective cohort study of octogenarians who lived in the mountain community of the Sirente geographic area in Central Italy. Malnutrition was operationalized according to the Global Leadership Initiative on Malnutrition (GLIM) criteria. Physical performance measures included the short physical performance battery (SPPB) and the isometric handgrip (IHG) test. Sarcopenia was operationalized as the coexistence of dynapenia and low appendicular skeletal mass, while frailty was identified using a modified Fried’s frailty phenotype. Linear regressions were conducted to examine the associations between malnutrition and physical performance tests. Binary regressions were performed to test the associations between malnutrition and both sarcopenia and frailty.</p> Results <p>Data of 364 older adults (mean age: 86.3 years) were analyzed. Malnutrition was significantly and inversely associated with IHG and walking speed (WS) performance, but not with other physical performance measures. No significant associations were found with sarcopenia or frailty.</p> Conclusions <p>Our results indicate that malnutrition is significantly associated with impairments in IHG and WS performance, but not with other well-established physical performance tests in octogenarian older adults. These data might be more closely associated with overall health impairments rather than isolated deficits in the neuromuscular system. Moreover, no significant associations were found between malnutrition and the prevalence of sarcopenia or frailty, which might reflect the fact that individuals examined in the present study were in a process of transition.</p>