Background and Objectives: High rates of psychiatric disorders and comorbidities have been reported in juvenile detainees which have been associated with repeat offenses. However, research on this topic has been limited to Asian countries. This study aimed to examine the prevalence of psychiatric disorders and sexual differences among juvenile detainees in a detention center in South Korea. Materials and Method: The participants comprised 54 males and 46 females, with a minimum intelligence score of 80. Psychiatric diagnosis was determined using the Mini-International Neuropsychiatric Interview for Children and Adolescents (MINI-KID). The Massachusetts Youth Screening Instrument-Version 2 (MAYSI-2) was used to investigate gender differences. Results: Using the MINI-KID, the most frequent diseases were conduct disorder (CD), alcohol dependence, suicidal tendency, attention-deficit/hyperactivity disorder (ADHD) with statistically significant differences between men and women. Only alcohol abuse was higher in men while the rest were higher in women. The items with a statistically significant gender difference in MAYSI-2, were alcohol/drug use, feeling depressed/anxious, somatic complaints, suicidal ideation, and traumatic experience. All items for which the gender difference was statistically significant were higher in the proportion of women. Conclusions: Juvenile detainees exhibit high rates of psychiatric disorders and comorbidities. CDs, alcohol dependence and ADHD are the most common psychiatric disorders among juvenile detainees in South Korea. Assessment of and intervention in psychiatric disorders may help prevent further offenses. These findings highlight the importance of diagnosing and intervening in psychiatric disorders within juvenile detention systems.