The purpose of this study was to investigate the association of affective temperament profiles and emotional and behavioural characteristics with Internet addiction among high school students. The study sample included 303 high school students. A sociodemographic characteristics data form, internet addiction scale (IAS), the strengths and difficulties questionnaire, and the temperament evaluation of Memphis, Pisa, Paris, and San Diego autoquestionnaire were used to collect data. Of the sample, 6.6% were found to be addicted to Internet. Having a computer in the home (P < 0.001) and using the Internet for more than two years (P < 0.001) were found to be related to higher scores on the IAS. The prevalence rate of anxious temperament for Internet addicts was more than that for nonaddicts (P < 0.001). Dysthymic (r = 0.199; P < 0.01), cyclothymic (r = 0.249; P < 0.01), hyperthymic (r = 0.156; P < 0.01), irritable (r = 0.254; P < 0.01), and anxious (r = 0.205; P < 0.01) temperaments; conduct problems (r = 0.146; P < 0.05), hyperactivity-inattention (r = 0.133; P < 0.05), emotional symptoms (r = 0.138; P < 0.05), and total difficulties (r = 0.160; P < 0.01) were found to be correlated with IAS scores. According to these findings, there is a relation between the Internet addiction and affective temperament profiles, especially with anxious temperament. Furthermore, emotional and behavioural problems are more frequent in adolescents who have problematic Internet use.