The EEGs of the 20 best behaved boys in a junior high school class of 131 boys were compared with the tracings of the 20 most troublesome boys in the class. These represented extremes from the point of view of behaviour and adjustment in a given situation. The age range of the two groups was the same (13-16½ years). Choice of boys over 13 years of age made comparison easier because adult patterns are then already established and consideration of normal year to year variations of tracings in children below this age was thus made unnecessary. Social, economic and cultural background was similar in the two groups, thus eliminating an important variable found in the groups compared in all previous studies by other authors. The boys in the most troublesome group were behaviour problems at home and in the neighborhood, as well as in the school situation. The boys in the so-called normal group presented no difficulties of behaviour in school, home or neighborhood. There were 12 abnormal tracings in the first group and 11 in the second. Intelligence level did not in itself have any influence on the nature of the tracings.The EEGs of the 10 best behaved and least delinquent boys in an institution for delinquent boys and the 10 most chronic delinquents with the most severe and chronic types of behaviour disorder were similarly compared. Four of the former and 9 of the latter 10 boys showed abnormal tracings.Results of comparison between intelligence, efficiency of performance and personality with type of EEG were also similarly contradictory, confusing and difficult to interpret. Individual case studies illustrated these contradictions and discrepancies over and over again.The most consistent incidence of abnormal EEGs was found in the most poorly behaved institution group, in the group with the severest and most chronic disorders of behaviour. This would suggest that the finding of an abnormal cortical electrical pattern may be indicative of a physiological disturbance which influences behaviour adversely. However, the very frequent presence of abnormal rhythms and patterns of the same kind found by us and by other observers in children without behaviour disorders and of normal and abnormal tracings in apparently similar types of behaviour problem children makes it difficult to interpret the significance of the findings in the individual case. The EEG is of course Valuable in the detection of hidden focal lesions and of cryptic epilepsy. The most that can be said at present for the value of other findings of dysrhythmia in behaviour problem children is that they may be regarded as a probable additional unfavorable personal factor, among many other factors, adversely influencing behaviour. Studies and results to date do not warrant further interpretation or clinical application in diagnosis, therapy or prognosis.Abstract Teaser