Background: Mild cognitive impairment (MCI) is an etiologically unclear disorder. Cerebrospinal fluid (CSF) biomarkers are potentially useful for the differentiation between various MCI etiologies. Aim: The aim of the study was to assess whether baseline CSF hyperphosphorylated tau (P-tau), total tau (T-tau), amyloid β 1–42 (Aβ42) and neurofilament light (NF-L) in patients with MCI could predict subcortical vascular dementia (SVD) and Alzheimer’s disease (AD) at follow-up. Methods: Biomarker levels were assessed by Luminex xMAP technology and ELISA. Results: Increased baseline concentrations of NF-L significantly separated MCI-SVD from stable MCI. The MCI-SVD patients were inseparable from stable MCI but separable from patients developing AD (MCI-AD) on the basis of Aβ42, T-tau and P-tau181 levels. Conclusion: A combination of the biomarkers Aβ42, T-tau, P-tau181 and NF-L has the potential to improve the clinical separation of MCI-SVD patients from stable MCI and MCI-AD patients.