In this issue of JAMA, 2 studies address the treatment and prognosis of patients with dementia. Quinn and colleagues1 describe results from a well-conducted trial conducted in conjunction with the Alzheimer's Disease Cooperative Study (ADCS) network designed to determine if treatment with the omega-3 fatty acid docosahexaenoic acid (DHA) improved the symptoms and course of patients with mild to moderate Alzheimer disease (AD). The multisite trial enrolled 402 patients (60% were assigned to DHA and 40% to placebo). At the end of the 18-month trial, there were no treatment group differences on any of the primary or secondary outcomes despite elevations of plasma phospholipids and cerebrospinal fluid DHA (measured in a subgroup). Among the 102 participants with baseline and follow-up brain magnetic resonance imaging, there were also no effects of treatment on total brain or hippocampal volume changes. However, among patients without an apolipoprotein E (APOE) ε4 allele, those assigned to DHA had less decline compared with those receiving placebo on 1 primary outcome and 1 secondary outcome.