Brain-derived neurotrophic factor (BDNF) is one of the key molecules modulating brain plasticity. While low circulating levels of BDNF have been suggested to predispose to Alzheimer's disease, very little data are available on its association with cognitive function in general population. We evaluated the association between plasma BDNF levels and cognition in a representative population sample of ageing men and women. The subjects (n=1389) were participants of the Dose-Responses to Exercise Training (DR's EXTRA) Study and represent a random sample of Eastern Finnish people (684 men and 705 women), 57-79 years of age at baseline of the study. Plasma BDNF levels were measured by enzyme-linked immunosorbent assay (ELISA). Cognitive function was evaluated using the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) neuropsychological test battery. Women had a higher mean (+/-SEM) plasma BDNF level than men (1721+/-55vs. 1495+/-54pg/ml, P<0.001). In women, 1 SD decrease in BDNF increased the risk for a low score in Naming Test by 53% (95% CI 1.21-1.92, P<0.001), in Mini-Mental State Examination by 63% (95% CI 1.21-2.20, P=0.001), in Word List Memory by 56% (95% CI 1.08-2.26, P=0.019), in Word List Recall by 50% (95% CI 1.10-2.05, P=0.010), in Word List Saving by 49% (95% CI 1.12-1.99, P=0.007), and in Word List Recognition by 64% (95% CI 1.19-2.25, P=0.002). Data were adjusted for age, education, depression, impaired glucose metabolism, cardiovascular disease, antihypertensive medication, lipid lowering medication, use of sex hormones, smoking, alcohol consumption, storing time of plasma in the freezer and platelet count. BDNF was not associated with cognition in men. Present data suggest that plasma BDNF is a biomarker of impaired memory and general cognitive function in ageing women.