Cognitive estimation was evaluated in patients with mild to moderate Alzheimer's disease (AD). In Experiment I, 25 AD patients and 16 normal controls generated estimates of real-world events. AD patients provided more extreme judgments than controls. Experiment II explored whether impaired word-finding contributed to the AD deficit by having subjects choose the 'best' answer to estimation questions. New samples of 14 AD patients and 12 normal controls were compared. AD patients selected the target responses less often than controls. These findings indicate that cognitive estimation is impaired in Alzheimer's disease. The potential contribution of semantic memory to cognitive estimation is discussed.