The cognitive and neuroimaging evolution over the course of dementia with Lewy bodies (DLB) from prodromal stage - Pro-DLB (subjective (SCI) to mild cognitive impairment (MCI)) - is poorly understood. The aim of this study was to analyze from 5-year longitudinal data the trajectories of Pro-DLB patients. The "Lewy- MEMENTO" prospective clinical cohort recruited 773 patients for either SCI or MCI. The Pro-DLB group was compared to a group with prodromal Alzheimer's disease (Pro-AD), a group with "prodromal DLB and AD" (Pro-DLB + AD), and a group without prodromal DLB and AD (no symptom [NS]). We modeled the 5-year evolution of cognitive functions and the 2-year evolution of brain MRI volumetry on MRI and brain metabolism (FDG PET). The Pro-AD and Pro-DLB + AD groups had more cognitive and functional decline than the Pro-DLB and NS groups (P < .001). The Pro-DLB group had more cognitive decline than the NS group (P < .004). Incident dementia during the follow-up was higher in the Pro-AD (13.0 per 100 person-years) and Pro-DLB + AD (10.3) groups than in the Pro-DLB (1.02) and NS (0.44) groups (P < .001). The decline in the metabolism of the left orbitofrontal cortex was greater in the Pro-DLB + AD group. The volume decrease of hippocampi, entorhinal cortices, amygdalae, and left insula was higher in the Pro-AD and the pro-DLB + AD groups. Patients in the pro-DLB group had less cognitive, functional, brain volume, and metabolism decrease than patients in the Pro-AD and pro-DLB + AD groups. DLB would therefore be a less degenerative and more dysfunctional disease at the prodromal stage.