Only boys were used in the analysis. Study subjects were drawn from a Danish birth cohort of all children born between Sept. 1, 1959, and Dec. 31, 1961, at Righospitalet in Copenhagen. The study hypothesized that boys who would become delinquents in the future would show excess delta and theta activity and slowing of the alpha frequency. The record of offenses in the Danish National Police Register (NPR) served as the measure of delinquency. The NPR contains information for the entire country and records all contacts of Danish police with individuals. A record in the register may result from even minor contact with the police. Lists for missing persons, lost passports, or admission to a psychiatric department were excluded from the analyses. Delinquency of study subjects mainly involved traffic and theft offenses, with a few instances of arrests for violent crimes. Electrodes were placed according to the 10-20 system over the right and left parietal, temporal, central, and occipital areas. Results showed that the relative amount of EEG activity at 8-10 Hz in 10-13-year-old Danish boys predicted officially registered recidivistic thievery. Results supported the second hypothesis--that slow alpha frequency predicts delinquency. However, the first hypothesis--that delta and theta activity would predict delinquency--was not supported. Two tables and about 25 references are included. (Author summary modified)