This study examined the frequency, predictors, and impact of sleep problems in a population-based sample of 205 Alzheimer's disease (AD) patients. Sleeping more than usual and early morning awakenings were the most common sleep problems reported but were the least disturbing behaviors for caregivers. Night-time awakenings were less common but were most disturbing to caregivers. Using logistic regression analyses, the factors most strongly associated with night awakenings among patients were male gender, greater memory problems, and decreased functional status. Patient depression increased the risk for caregivers to rate patient sleep problems as more disturbing overall. Cluster analyses revealed three characteristic groups of patients who awakened caregivers: one group was inactive during the day but had few other behavior problems; one group had increased levels of fearfulness, fidgeting, and occasional sadness; and the third group had multiple behavior problems, including frequent episodes of sadness, fearfulness, inactivity, fidgeting, and hallucinations. These findings indicate that the nature of sleep problems in AD is multifaceted; future research on the occurrence and treatment of sleep disturbance in dementia patients should consider the patterns of individual differences that may influence its development.