Over the past few years, circulating cell-free DNA (cfDNA) research has grown exponentially. Several studies have associated the release of cfDNA in the bloodstream, cerebrospinal fluid, and other body fluids with increased apoptosis and cell death. Therefore, their possible use as biomarkers for cancer and other diseases has emerged. The diagnosis of pathological entities such as schizophrenia and neurodegenerative diseases involves many challenges and requires ruling out conditions with similar symptoms. In this context, cfDNA could serve as a valuable diagnostic biomarker. This study encompasses the recent bibliography and research regarding the utilization of circulating cfDNA for diagnostic purposes in schizophrenia, Alzheimer's disease, Parkinson's disease, multiple sclerosis, amyotrophic lateral sclerosis, and Huntington's disease. This minimally invasive method has provided important evidence regarding the diagnosis of the aforementioned diseases although further research is necessary.