Communication and information sharing are among the basic pillars of education, the economic sphere and leisure activities in modern society. The mass introduction and use of information and communication technologies (ICT) makes life much easier, but it also poses certain risks. These are, in particular, states of mental discomfort associated with situations in which these modern links are not available or access to them is restricted. Furthermore, a person is endangered by the development of compulsive behavior and possible dependence of the behavioral type on a mobile communicator - nomophobia. Developed nomophobia affects all attributes of human health, seriously affecting its mental, physical and social components. As children encounter modern ICT at an early age at home, at school and in leisure activities, they soon learn to handle it and ICT becomes a natural part of their world. However, the speed of mastering the manipulation of ICT lags behind the preventive action that would prepare children and adolescents for encounters with risky moments and offer their effective prevention and solution. The main goal of the research was to determine the degree of dependence of a sample of secondary school pupils on mobile devices, the partial goal was to map potentially risky areas associated with the use of ICT. Three working hypotheses were established, which concerned the comparison of opinions, behavior and the degree of nomophobia between boys and girls. A quantitative method was chosen to meet the objective of the survey, and an anonymous questionnaire was used as a tool. The questionnaire contained a standardized core for determining the degree of nomophobia (Yildirim & Coreria, 2015; University of Iowa). It included 20 items focused on respondents' reactions in situations where ICT links are not available or cannot be used. The questionnaire was supplemented with items used to find out which applications respondents often use, how they handle them and what their preferences are in this respect. First, a preliminary survey was conducted in a small sample of 22 pupils, which verified whether the proposed questionnaire is understandable. The survey itself took place in the eighth and ninth grades of 11 intentionally selected primary schools in the Hradec Králové region. Data were obtained from a set of 373 respondents with a balanced representation of boys and girls. The answers of the respondents were evaluated by methods of descriptive statistics, Student's t-test was used to analyze the hypotheses. No personal data was collected, pupils were informed in advance about the purpose of the study, and they could refuse to complete the questionnaire. The results showed that 0.5% of respondents did not show symptoms of nomophobia, its very mild and moderate form was recorded in 70% of respondents, mild in 18% of the group, moderate in 8% and severe in 2% of respondents. Almost three quarters of pupils are not directly at risk of dependence on mobile devices. Although they use ICT intensively, they feel only a slight nervousness when they are unavailable. However, a tenth of the sample shows serious problems of a behavioral nature. Respondents use an average of 4 applications, in particular the Messenger communication program, the social networks YouTube, Instagram and Facebook, and the Spotify music playback application. When testing hypotheses concerning the differences in the behavior of boys and girls, statistically significant differences were found in 6 items, but not in 14 items. The girls in the sample show a higher degree of nomophobia than the boys. The biggest differences in responses were noted mainly for fears of not being able to communicate immediately with family or friends.