Background <p>Previous almond intervention studies involving relatively healthy populations did not demonstrate improvements in cognitive performance. However, a long-term study with participants at risk of cognitive decline, such as those with prediabetes, may be necessary. Potential changes in cognitive performance could be related to changes in brain vascular function.</p> Methods <p>A randomized, single-blinded, controlled crossover trial including 43 overweight/obese men and women with prediabetes. Participants were assigned to a 5-month almond (50 g/day) intervention and a 5-month control period, separated by a 2-month washout. Cognitive performance (psychomotor speed, executive function and memory) was assessed using the Cambridge Neuropsychological Test Automated Battery (CANTAB) at the beginning and at the end of each period. Cerebral blood flow (CBF), a marker of brain vascular function, was measured using the non-invasive magnetic resonance imaging (MRI) perfusion method, pseudo-continuous Arterial Spin Labeling (pCASL) at the end of each study period. Data were analyzed using linear mixed models.</p> Results <p>Participants had a median age (interquartile range [IQR]) of 66 years (IQR: 59–69 years), and their median BMI was 28.3 kg/m² (IQR: 26.7–33.1 kg/m²). Thirty-four prediabetic adults (22 men and 12 women) completed the study. No significant intervention effects were observed on any cognitive performance outcomes (<i>n</i> = 33). Compared to the control period, long-term almond consumption also had no significant impact on whole-brain or regional CBF (<i>n</i> = 26).</p> Conclusion <p>In line with earlier observations in relatively healthy populations, long-term almond consumption (50 g/day) did not enhance cognitive performance in overweight/obese individuals with prediabetes. Moreover, brain vascular function was unaffected.</p>