THE DATA WERE GATHERED FROM QUESTIONNAIRES AND INTERVIEWS FROM 57 MALE AND 21 FEMALE GANG MEMBERS WHO HAD ATTENDED GROUP DISCUSSION SESSIONS AT A COPENHAGEN YOUTH CLINIC. THE ANALYSIS COVERS THE STRUCTURE OF THE GANG--ITS LEADERS, MEETING PLACES, CHANGING SIZE, RATIO OF GIRLS TO BOYS--BUT FOCUSES ON THE CRIMINAL ACTIVITY OF MALE MEMBERS BEFORE, DURING, AND AFTER GANG MEMBERSHIP. THE CRIME ACTIVITY ANALYSIS FOLLOWS THE YOUTHS FROM CHILDHOOD TO ADULTHOOD, COVERING 8 YEARS BEFORE THE GANG WAS FORMED, AN 18-MONTH PERIOD OF GANG ACTIVITY (JULY 1962 TO DECEMBER 1963), AND A 13-YEAR FOLLOWUP PERIOD ENDING IN JANUARY 1977. THE MAIN ACTIVITIES OF THE GANG WERE DELINQUENT OR CRIMINAL ACTS, PREDOMINANTLY CAR THEFTS ENGINEERED BY TWO OR THREE BOYS. MANY OF THE BOYS HAD COMMITTED CRIMES BEFORE THEY JOINED THE GANG AND CONTINUED THEIR CRIMINAL ACTIVITY AFTER THEY LEFT THE GANG. HOWEVER, THE FOLLOWUP STUDY FOUND THAT 86 PERCENT HAD BEEN CRIME-FREE FOR 6 YEARS, 74 PERCENT FOR 11 YEARS. THE MAJORITY OF BOYS WERE INVOLVED ONLY IN A FEW, NOT VERY SERIOUS CRIMINAL ACTIVITIES DURING THEIR GANG PARTICIPATION, BUT A FEW WERE INVOLVED RATHER HEAVILY IN CRIME AT THAT TIME. THE SAME PICTURE EMERGES FOR THE FOLLOWUP PERIOD. HOWEVER, OF THE FIVE BOYS MOST CRIMINALLY ACTIVE DURING THE GANG PERIOD, ONLY TWO CONTINUED THEIR DELINQUENCY AFTER 1964, WHEREAS SOME OF THE BOYS WHO WERE NOT VERY ACTIVE DURING THEIR GANG MEMBERSHIP CONTINUED THEIR CRIMINAL ACTIVITY. THE DATA DO NOT LEND THEMELVES TO CONCLUSIONS ABOUT CAUSES AND CONSEQUENCES--WHETHER GANG MEMBERSHIP INCREASES THE RISK OF CRIMINALITY IN LATER LIFE. TABULAR DATA AND SUGGESTIONS FOR FUTHER RESEARCH ARE INCLUDED. (LKM)