Male and female Puerto Rican children born in 1970 were traced through the greater San Juan police departments, charting the incidence of delinquency and the number of recurring offenders. A research design, measurement approach, and statistical analysis framework were used. Results indicate that males are more likely than females to be delinquent and to be delinquent recidivists. Males predominate both in overall delinquency and in serious offenses. Delinquency does not begin very early or late in the juvenile age span but mostly begins in the middle years. There are good indications that the authorities, such as the police and courts, have responded successfully to the offenders in the 1970 cohort. Finally, delinquency in the 1970 cohort is a very different phenomenon from that in the two well-known Philadelphia studies done in 1945 and 1958. It appears that the authorities exhibited an earlier and a more effective response to the delinquents in Puerto Rico than was the case in Philadelphia. 160 tables, 3 figures, 10 references, and appendix