"Sundowning," a term that is sometimes equated with sleep disturbance or nocturnal delirium in dementia, is a poorly understood psychiatric phenomenon. In this study, we performed systematic, temporally specific, behavioral observations of nine profoundly demented nursing home patients 4 times an hour over a 12-hour period (1300 to 0100h) to determine whether their agitation was more likely to occur at a particular time of day. Results indicated only equivocal evidence that agitation was any worse nocturnally or during the time near sunset, thus raising the possibility that at least some components of sundowning may reflect disruptive behaviors occurring with identical frequency throughout the day but with differential impact upon nursing staff. Additional data indicated that awakening from sleep during darkness was also associated with agitation. A final result was a trend indicating the apparent worsening of agitation seasonally (greater agitation during winter), which may suggest involvement of the circadian timing system.