We all know what internet is and the definition of the Internet in Croation national dictionary is that "the Internet is a network that connects numerous computer systems and networks, based on a common address system and communication protocol. Internet give great opportunity to all of us and provided various possibilities, because thanks to it we can get the information and make connections in just a few seconds. From the number of the world's population (7.9 billion), the number of Internet users by 2022 is about 5.3 billion which means that 67% of world polulation has access to internet. The prevalence of the Internet in Croatia which is relatively small europian country (3,85 million inhabitants) reached 3,787,838 users. Its means that almost every household in Croatia (98.3%) have internet connection. Adolescence is the phase of life between childhood and adulthood, from ages 10 to 19. It is a unique stage of human development and an important time for laying the foundations of good health. Adolescents experience rapid physical, cognitive and psychosocial growth. Many studies shows that adolescents spend most of their time on the Internet watching videos, listening to music, searching for learning information, reading the news, messaging through applications, and playing online games. We should not ignore the fact that, although it is available to all people around the world, it can also cause damage to users if it falls into the hands of criminal person. The definition of addiction according to the 10 th Revision of the International Classification of Diseases and Related Health Problems is: addiction is "a group of behavioral, cognitive, and physical changes that develop after repeated use of certain substances, and regularly include a strong desire to take that substance and difficulties in controlling its intake" (WHO, 2012). Internet addiction does not exist as an official diagnosis in the 5 th edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM V), nor does it exist in the 10 th edition of the International Classification of Diseases and Related Health Problems (ICD-10), although the prevalence of this disorder according to some scientific researches is estimated at 6.3–37.9% in Asia; 0.3–8.2% in America; 1 –21.3% in Europe.