Patients with lesions to posterior cortex were compared to controls, matched for age and education, on tests on sustained attention. One test was a simple reaction time task requiring subjects to respond whenever they saw an 'X'. The other was a Continuous Performance Test that required subjects to respond to an 'X' but refrain from responding to other letters. The patients missed more targets than control subjects on both tests. On the Continuous Performance Test the difference between patients and controls increased with time on task, suggesting a sustained attention deficit similar to that previously observed in patients with right frontal lesions. However, whereas frontal patients showed a tendency toward greater impairment when the rate of stimulus presentation was relatively slow, the posterior patients performed significantly worse when the stimuli were presented at a faster rate.