Within-person trajectories of cerebrospinal fluid (CSF) biomarkers in Alzheimer's disease (AD) are not well defined. We included 467 subjects from the BIOMARKAPD study with at least two serial CSF samples. Diagnoses were subjective cognitive decline (n = 75), mild cognitive impairment (n = 128), and AD dementia (n = 110), and a group of cognitively unimpaired subjects (n = 154) were also included. We measured baseline and follow-up CSF levels of total tau (t-tau), phosphorylated tau (p-tau), YKL-40, and neurofilament light (NfL). Median CSF sampling interval was 2.1 years. CSF levels of t-tau, p-tau, NfL, and YKL-40 were 2% higher per each year of baseline age in controls (P <.001). In AD, t-tau levels were 1% lower (P <.001) and p-tau levels did not change per each year of baseline age. Longitudinally, only NfL (P <.001) and YKL-40 (P <.02) increased during the study period. All four CSF biomarkers increase with age, but this effect deviates in AD for t-tau and p-tau. •In this large longitudinal multicenter cerebrospinal fluid (CSF) study each year of increase at baseline age was significantly associated with 2% higher mean CSF t-tau and p-tau levels in controls. Within the Alzheimer's disease group, each year of increase at baseline age was significantly associated with 1% lower mean CSF t-tau levels, and p-tau levels did not change with age.•Each year of increase at baseline age was significantly associated with 2% higher mean CSF neurofilament light (NfL) and YKL-40 levels in controls without differences among groups.•Longitudinally, after adjusting for baseline age, only NfL and YKL-40 levels significantly increased during the study period in all groups.•The pattern of change of CSF tau, NfL, and YKL-40 is different in Alzheimer's disease.