This study investigated whether internet addiction is related to gender, academic achievement, duration of internet use, loneliness and shyness. The study was carried out with 206 adolescents aged between 15-18 years (X=16.50) and studying public high schools. 55.8% (115) of the participant students are female and 44.2% (91) are male. To collect data, the "Personal Information Form" developed by the researchers, the "Internet Addiction Scale" developed by Young (1998), the "UCLA Loneliness Scale" developed by Russel, Peplau and Cutrona (1980), and the "Shyness Scale" developed by Cheek and Buss (1981) were used. The results indicated that internet addiction changed according to gender, academic achievement and duration of internet use. Moreover, while academic achievement significantly and negatively predicted internet addiction, duration of internet use and shyness significantly and positively predicted internet addiction. However, the variables of gender and loneliness were found to have no significant effects on internet addiction.