To estimate the frequency of borderline personality disorder (BPD) in French high school students. A random sample of high school students (n = 1363) ranging in age from 13 to 20 years agreed to complete a questionnaire, the Screening Test for Comorbid Personality Disorders (STCPD); 107 of them volunteered to be interviewed. We assessed this group using the Revised Diagnostic Interview for Borderlines (DIB-R). We conducted a regression analysis to determine a cut-off for BPD diagnosis with the STCPD. We estimated the overall frequency of BPD to be 10% for boys and 18% for girls. After a peak of frequency at age 14 years for both sexes, the frequency increased significantly again in late adolescence. This study found a high frequency of BPD in French adolescents, which adds to questions regarding the validity of diagnosing this disorder in adolescents.