BACKGROUND: The effectiveness of nutritional supplementation in improving cognitive functioning is evaluated in elderly people. METHODS: The authors systematically reviewed randomized controlled trials that compared nutritional supplementation with a placebo treatment. Trials were identified from a MEDLINE search and from reference lists of identified studies and review articles. From each trial, information was gathered on the number and age of persons studied; the type, dosage, and duration of the intervention; and the assessed outcome measures. RESULTS: From 1086 titles, 571 articles were excluded based on their titles. Of the remaining 467 articles, the abstracts were read and 422 articles were excluded based on information found there. The remaining articles were screened for quality aspects of the study design, leaving 21 proper randomized, controlled trials. These trials are discussed in three groups according to the type of supplementation: multinutrient intervention or single components with or without a putative mechanism. Twelve studies, which were evenly distributed among the three supplement groups, found significantly positive effects of nutritional intervention on cognitive functioning, whereas nine studies did not. None of the studies found a significantly negative effect of nutritional intervention. CONCLUSIONS: Shortcomings in methodology varying from the duration of intervention to outcome measures partly explain discrepancies in findings. Despite the heterogeneity in trial design, the results of this review suggest that nutritional supplements may improve the cognitive functioning of elderly persons and do no harm. Further well-designed studies are needed to support these findings.