Due to supporting evidence that dietary patterns may have a significant role in the maintenance of good physical performance with aging, we tested whether plasma fatty acids, saturated fatty acids (SFA), and polyunsaturated (PUFA) fatty acids are cross-sectionally associated with different physical performance and predict changes in physical performance over a 3-year period. Data were from the InCHIANTI study, a population-based study of older Italians. Plasma fatty acids were measured at enrollment (1998-2000), and outcome variables, Summary Physical Performance Battery (SPPB), and time to walk 7 meters (m) were measured at enrollment and after 3 years (2001-2004). At enrollment, 330 participants had significantly impaired lower extremity performance (defined as a SPPB score < or = 9). Adjusting for age, participants with a SPPB score > 9 had higher levels of total PUFA, n-3 PUFA, and n-6 PUFA, while significantly lower levels of SFA than those with a SPPB score < 9. Baseline SPPB scores were also associated with n-3 PUFA (beta = 0.148, p = 0.031), whereas the 7-m walk time was associated with total PUFA (beta = - 0.068, p = 0.008), after adjusting for potential confounders. Of the 884 participants with a SPPB score > 9 at baseline, 114 (12.9%) developed impaired lower extremity performance (SPPB < or = 9). In fully adjusted logistic models, baseline n-3 PUFA levels were inversely related to the risk of developing a decline in SPPB to < or = 9 (odds ratio [OR] = 0.21; 95% confidence interval [CI] = 0.08-0.53), while the n-6/n-3 ratio was associated with a higher risk of SPPB decline to < or = 9 (OR = 5.23; 95% CI = 2.02-13.51). In multivariate regression models, the n-6/n-3 ratio was associated with a longer time to walk 7 m (beta = 0.396, p = 0.037). n-3 PUFA plasma levels, which most likely reflect dietary intake, seem to protect against accelerated decline of physical performance. A higher n-6/n-3 ratio was associated with higher risk of developing poor physical performance and slower walking speed.