This study aims: a) to estimate the prevalence of internet addiction among adolescents of urban and rural areas in Greece, b) to examine whether the Internet Addiction Test cut-off point is applicable to them and c) to investigate the phenomenon's association with academic achievement. Participants were 2090 adolescents (mean age 16, 1036 males, 1050 females). Young's (1998) Internet Addiction Test and her Diagnostic Questionnaire were applied. School records' grades were retrieved. A 3.1% prevalence revealed, while boys {F (1, 1642) = 6.207, p less than 0.05}, urban residents {F (1, 1642) = 5.53, p greater than 0.05} and academic track high school students {F (1, 1642) = 5.30, p less than 0.05} were at higher risk. An Internet Addiction Test score of 51 points (sample's mean = 27.69, SD = 17.38) was proposed as the optimal cut-off point combining high sensitivity (98%) and specificity (91%). Finally, findings illustrated the syndrome's relation to worse academic achievement {F (1, 1725) = 0.93, p greater than 0.05}. (Contains 7 tables and 1 figure.)