The aim of the study was to determine the relationship between the symptoms of mobile phone addiction and young people's involvement in the Internet.

The following self-constructed instruments were used in this study: a socio-demographic questionnaire, the Mobile Phone Addiction Assessment Questionnaire, and the Internet Addiction Assessment Questionnaire. The participant group consisted of 291 persons aged 13–19 years.

The result show that there are statistically significant relationships between

1. (1) The frequency with which the young people use Internet pornography, instant messengers and Internet websites, play aggressive computer games and look for acceptance and understanding exclusively on-line and

2. (2) The scales of the Mobile Phone Addiction Assessment Questionnaire.

1. 1. Addiction to text messaging and making mobile phone calls and the preference for forming interpersonal relationships and expressing emotions via phone calls and texting co-occur with symptoms of Internet addiction, playing aggressive computer games, using on-line pornography, and the belief that it is only on-line that one can gain acceptance and understanding and express authentic emotions.

2. 2. In the group of boys, the strongest relationship was found between addiction to mobile phone calls and text messages and the use of on-line pornography.

3. 3. In the group of girls, the strongest relationship was found between addiction to the Internet and the preference for forming interpersonal relationships and expressing emotions via text messages and phone calls.