The increased time spent using the Internet and smartphones is prevalent primarily among adolescents. This group is currently of particular interest to media educators and psychologists studying the impact of ICTs on quality of life. An example of the negative changes associated with the intensive computerisation of various spaces is the uncontrolled and inadequate use of the Internet, referred to as problematic Internet use (PUI). This text contributes to the discussion on the extent of PUI among adolescents (12–16 years) in the Czech Republic (N=1555), Poland (N=501), and Slovakia (N=478). Based on the collected data, it was found that: 1) Polish and Czech adolescents are similar in terms of the intensity of PUI symptoms (adolescents from Slovakia are characterised by lower levels of PUI); 2) The vast majority of young people do not exceed PUI thresholds that could be considered alarming; 3) Lack of sleep or neglecting meals in favour of Internet use are the least frequent factors in the study group; 4) Most often adolescents declare that they are bored when they do not have access to the Internet; 5) Adolescents are a nonhomogeneous group in terms of the intensity of occurrence of PUI traits, but only 0.3% of adolescents in the Czech Republic and 0.4% in Poland had all 6 PUI factors present in maximum intensity.