The term "executive functions" was coined to describe the abilities of planning, monitoring and controlling activity, specially in novel tasks. These functions have been associated with the activity of the frontal lobes. Dysexecutive function results in impaired inhibition of non-relevant information, flexibility and updating mental representations which can be observed in behaviour and in executive tests. The assessment of executive control is necessarily indirect and executive tasks always include non-executive components. Therefore, disturbances in executive tests are neither sensible nor specific for frontal lobe dysfunction. The results on different executive tasks are frequently dissociated in the same patient and are weakly correlated with the behavioural disturbances. Thus, the results on executive tests should always be compared to behavioural assessment.