This narrative review examines serum biomarkers for the diagnosis and monitoring of delirium. Serum biomarkers for delirium fall into three major groups: 1) those that are present or elevated prior to disease onset-risk markers, 2) those that rise with onset and fall with recovery-disease markers, and 3) those that rise in proportion to the consequences of disease-end products. As risk markers, we examine serum chemistries and genetic risk markers. As disease markers, we examine serum anticholinergic activity, amino acids, melatonin, cytokines, cortisol, and gene expression. As end products of delirium, we examine markers of neuronal injury. Finally, we discuss methodological and biostatistical considerations for future biomarker studies. Identifying accurate biomarkers for delirium may shed further light into its pathophysiology and on the interrelationship between delirium and dementia.