A 84-year-old male exhibited sleep-onset rapid eye movement period (SOREM) during diurnal electroencephalogram recording in the course of hypoactive delirium. Factors such as aging, dementia of Alzheimer type, lacunar infarcts, and a common cold seemed to be involved in this delirious episode lasting several days. No dream experience was reported right after this SOREM. No SOREM was recorded from this case after recovery from delirium. This case provides evidence indicating that SOREM may occur not only in hyperactive delirium-like delirium tremens, but also in hypoactive delirium with mild-to-moderate severity. Diurnal recording, as well as nocturnal polysomnography, might also be important when studying SOREM during hypoactive delirium.