CSF Aβ42/Aβ40 and tau phosphorylated at site 181 (p-tau181) are well-established biomarkers of Alzheimer disease (AD). This study used mass spectrometry to measure concentrations of 9 phosphorylated and 5 non-phosphorylated species, and phosphorylation occupancies (phosphorylated/non-phosphorylated [%]) at 10 sites. In 750 individuals with a median age of 71.2 years, CSF pT217/T217 (%) predicted amyloid PET status slightly better than Aβ42/Aβ40 (p=0.02). In amyloid PET positive individuals (n=263), CSF pT217/T217 (%) was more strongly correlated with amyloid PET Centiloid (Spearman ρ=0.69) than Aβ42/Aβ40 (ρ = -0.42, p