Objective: To investigate the effect of a medical food on cognitive function in people with mild Alzheimer's disease (AD). Methods: A total of 225 drug-naïve AD patients participated in this randomized, double-blind controlled trial. Patients were randomized to active product, Souvenaid, or a control drink, taken once-daily for 12 weeks. Primary outcome measures were the delayed verbal recall task of the Wechsler Memory Scale-revised, and the 13-item modified Alzheimer's Disease Assessment Scale-cognitive subscale at week 12. Results: At 12 weeks, significant improvement in the delayed verbal recall task was noted in the active group compared with control (P = .021). Modified Alzheimer's Disease Assessment Scale-cognitive subscale and other outcome scores (e.g., Clinician Interview Based Impression of Change plus Caregiver Input, 12-item Neuropsychiatric Inventory, Alzheimer's disease Co-operative Study-Activities of Daily Living, Quality of Life in Alzheimer's Disease) were unchanged. The control group neither deteriorated nor improved. Compliance was excellent (95%) and the product was well tolerated. Conclusions: Supplementation with a medical food including phosphatide precursors and cofactors for 12 weeks improved memory (delayed verbal recall) in mild AD patients. This proof-of-concept study justifies further clinical trials. © 2010 The Alzheimer's Association.