The effect of low serum 25(OH)D on cognitive function is difficult to determine owing to the many factors that can influence these relationships (e.g., measurements, study design, and obesity). The primary purpose of this review was to synthesize the current evidence on the association between serum 25(OH)D and cognition giving special consideration to specific influential factors. A search was conducted in PubMed for studies published between 2010 and 2018 using terms related to serum 25(OH)D and cognition. Only studies that used liquid chromatography tandem-mass spectrometry (LC-MS) were included, since this is considered the 'gold standard method', to measure serum 25(OH)D. Of the 70 articles evaluated, 13 met all inclusion criteria for this review. The majority of the observational and longitudinal studies demonstrate a significant association between low serum 25(OH)D and compromised cognition. However, two randomized controlled trials showed inconsistent results on the impact of vitamin D supplementation on cognitive function. The varied methodologies for ascertaining cognition and the inclusion or exclusion of confounding variables (e.g., obesity, sunlight exposure) in the statistical analyses make drawing conclusions on the association between serum 25(OH)D and cognitive functioning inherently difficult. Despite the known higher occurrence of serum 25(OH) deficiency among minority populations, the majority of studies were conducted in with White participants. In order to more clearly discern the relationship between serum 25(OH)D and cognitive functioning, future studies should target more diverse study populations and utilize comprehensive measures to reliably capture cognition, as well as important known determinants of serum 25(OH)D.