The objectives of this study were to investigate the association of four plasma biomarkers – amyloid‐beta (Aβ)42/40, glial fibrillary acidic protein (GFAP), neurofilament light (NfL), and phosphorylated tau 181 (pTau181) – and disease progression in MCL‐LB measured by: (1) conversion to dementia/death and (2) cognitive performance. Here, GFAP is linked to dementia.