Measures of verbal fluency are widely used in the assessment of cognitive functioning of the elderly. However, limited research has evaluated patterns (across specific timed intervals) of performance on tasks of language fluency in different forms of dementia. The current study investigated semantic fluency in 488 elderly individuals (249 with Alzheimer's dementia, 97 Vascular dementia, 97 Mild Cognitive Impairment and 45 cognitively intact) across 15-second intervals in an animal naming task using retrospective chart review. Normal controls produced significantly more exemplars and AD patients produced fewer animal names than the other groups. After the first 15- second time interval, the demented groups produced significantly fewer exemplars than the non-demented. At the end of 30 seconds it was possible to differentiate normal aging from MCI who no longer differed from the VaD group. Overall, it appears that the greatest and most clinically meaningful differences between the diagnostic groups were detected in the first three 15-second intervals. The present findings support the use of time intervals and total scores on tasks of verbal fluency in clinical settings and for research purposes.