The objective of this study was to evaluate the biogenetic temperament and character profiles in Korean adolescents with problematic Internet use. Six hundred eighty-six high school students completed the Internet Addiction Test (IAT), Junior Temperament and Character Inventory (JTCI), and Conners/Wells Adolescent Self-Report Scale: Short Form (CASS: Short). The problematic Internet use group showed higher scores in the Self-Directedness and Cooperativeness profiles and lower scores in the Novelty Seeking and Self-Transcendence profiles of the JTCI, compared with the nonproblematic Internet use group, after controlling for the ADHD symptoms. The results of this study suggest that temperament/character patterns should be considered in accounts of the etiology of problematic Internet use.