THE STUDY IS CONCERNED WITH ILLUSTRATING THE EXTENT TO WHICH RECIDIVISM RATES CAN VARY GIVEN DIFFERENT DEFINITIONS OF TWO VARIABLES: CRITERION MEASURE AND LENGTH OF FOLLOWUP PERIOD. STUDY SUBJECTS ARE 1,806 FEDERAL PRISONERS SERVING A MAXIMUM TERM OF MORE THAN 1 YEAR AND 1 DAY WHO WERE RELEASED TO THE COMMUNITY DURING THE FIRST 6 MONTHS OF 1970. ALL MAJOR FORMS OF RELEASE -PAROLE, MANDATORY RELEASE, EXPIRATION OF SENTENCE -- ARE INCLUDED. FOUR DIFFERENT CRITERION MEASURES (NEW ARRESTS, NEW CONVICTIONS, NEW COMMITMENT OF 60 DAYS OR MORE, NEW COMMITMENT OF MORE THAN 1 YEAR) AND SIX FOLLOWUP PERIODS (1 THROUGH 6 YEARS AFTER RELEASE) ARE EMPLOYED IN CALCULATIONS OF RECIDIVISM RATES FOR THE STUDY GROUP. BOTH CRITERION MEASURE AND LENGTH OF FOLLOWUP PERIOD HAVE CONSIDERABLE IMPACT ON THE RECIDIVISM RATE. FOR EXAMPLE, AFTER 1 YEAR, THE RECIDIVISM RATE VARIES FROM 29 TO 8.7 PERCENT DEPENDING UPON WHETHER NEW ARREST OR NEW PRISON COMMITMENT OF MORE THAN 1 YEAR IS USED AS THE CRITERION MEASURE. AFTER 6 YEARS, THE FORMER CRITERION PRODUCES A RECIDIVISM RATE OF 60.4 PERCENT, COMPARED TO 27.5 PERCENT FOR THE LATTER. THE RECIDIVISM RATE FOR THE NEW ARREST CRITERION VARIES FROM 29 PERCENT AT 1 YEAR, TO 43.7 PERCENT AT 2 YEARS, TO 60.4 PERCENT AT 6 YEARS. FOR NEW COMMITMENT OF 1 YEAR OR MORE, THE RATE VARIES FROM 8.7 PERCENT AT 1 YEAR, TO 15.8 PERCENT AT 2 YEARS, TO 27.5 PERCENT AT 6 YEARS. IF BOTH CRITERION MEASURE AND FOLLOWUP PERIOD ARE CONSIDERED, THE RECIDIVISM RATE COULD VARY FROM 8.7 PERCENT (NEW COMMITMENT OF MORE THAN 1 YEAR, FOLLOWUP) TO 60.4 PERCENT (NEW ARREST CRITERION, 6-YEAR FOLLOWUP). SUPPORTING DATA ARE INCLUDED (LKM)