The aim of the study was to compare the severity of symptoms of mobile phone addiction in adolescents at risk of Internet addiction and those at no risk of such addiction.

The study was conducted using two self-constructed questionnaires, a socio-demographic questionnaire and the Mobile Phone Addiction Assessment Questionnaire, and Young's Internet Addiction Test.

The participant group included 291 persons aged 13–19 years.

Based on the Internet Addiction Test, a group of 109 persons meeting Young's criteria for the risk of Internet addiction and a group of 154 no-risk participants were singled out.

1. 1. Young people at risk of Internet addiction, significantly more often than no- risk participants, made unsuccessful attempts at limiting the number of phone calls and text messages, reduced their sleeping hours to be able to talk on the phone, paid very high bills which exceeded their calling and texting plans, kept the costs of phone calls secret from their families, played down the number of mobile phone calls they made, and had another, spare mobile phone.

2. 2. Young people at risk of Internet addiction, significantly more often than no risk participants, felt lonely and unaccepted when they did not receive phone calls and text messages, preferred to form interpersonal relationships and express their emotions by means of telephone calls and text messages, and used their mobiles to listen to music, take videos and photos, play games and access the Internet.