Neurobiology is regulated by miRNA. Here circulating plasma miRNAs were assayed on a 754 miRNA OpenArray platform using 90 monozygotic elderly twins (73–95 year of age) and associated with mini mental state examination (MMSE) and a five-component cognitive score (CCS) in an explorative study. Both ordinary individual and twin-pair analyses were performed with level of cognitive scores. Candidate miRNAs were further associated with cognitive decline over 10 years using up to six repeated assessments. A total of 278 miRNAs were expressed in plasma from at least ten participants and 23 miRNAs were nominally associated (i.e., at an uncorrected p < 0.05) with CCS or MMSE in the paired analyses. Generally, elderly individuals with poor cognitive function had increase miRNA expression compared with equivalent individuals who performed better on the cognitive scale. Three miRNAs, miR-151a-3p, miR-212-3p and miR-1274b were associated with CCS both in the paired and the individual analysis. Four miRNAs found to be associated with CCS in cross-sectional analysis were also found to show an association in longitudinal analysis such that increase miRNA expression was associated with steeper cognitive decline. We propose a shared biological path underlies dementia and normative cognitive aging.