In this prospective study of the differences between the epileptic syndrome of absence attacks in the child (EAN) and the syndrome of juvenile absence attacks (EAJ), the author considers the characteristics of these syndromes in order to differentiate their various aspects, namely clinical features, complementary tests, course and prognosis. These cases are from a series of 6,299 epileptic patients. One of the objectives of a prospective study begun in 1970 was to evaluate the clinical course of all cases in which valproic acid was used. Valproic acid is known to be most effective in the basic crises of these two syndromes, namely the typical absence attacks. It is therefore an analysis of the clinical features and their subsequent course and prognosis when thus treated, since a retrospective study including a much larger number of patients would not be considered to be satisfactory in view of the 'bias' due to only some patients having access to treatment with this drug. The author analyzes 138 cases of EAN and 42 cases of EAJ seen between 1970 and the end of 1995. These syndromes, particularly EAN, have always been considered to have an excellent prognosis. The author tries to show from the point of view of long term follow-up, that absence attacks may not only persist into adult life but also be associated with other types of crises which worsen the prognosis. Thus, for instance, in EAN 50% of the cases show generalized tonic-clonic seizures on long-term follow-up. In EAJ the corresponding figure is 76.1%. This data modifies previous ideas as to the benign course of these syndromes when they are followed-up for a long period. The basic criteria were: a first visit after 1970 and an age of onset between 3 and 10 years for EAN and over 10 years for EAJ. In all cases there was the following conditions, onset by absence attacks, lack of permanent neurological or psychological disorders, and a video-EEG recording of a typical generalized EEG during an attack.