Since 1985, early changes in the EES have been demonstrated in the course of HIV infection. This method can be considered one of the accurate tests for the assessment of evolution of the disease. Abnormal anterior changes are present in about 30% of HIV+subjects with at least stage II disease. EEG abnormalities during the disease form a spectrum ranging from minor changes to slow diffuse activity, usually found in cortical lesions. These are associated in some cases with a periodic or pseudo-periodic activity as often found in white matter lesions.