The internet was originally designed to facilitate communication and research activities. However, the dramatic increase in the use of the internet in recent years has led to pathological use (Internet addiction disorder). The adolescent population is highly prone to internet addiction and this can affect their personal, family, academic, interpersonal and social life. The aim of this study was to evaluate the internet addiction disorder on adolescents' students. Research design: A Descriptive design was used in this study. Setting: The study was conducted at all secondary schools for girls at Benha City they named; Benha Secondary School, El Shimaa Secondary School, and Om Elmoamneen Secondary School. The sample included 200 secondary female students they were selected as systematic random sample from studied schools. Tools: A structured interviewing questionnaire consisted of five parts 1) the socio-demographic characteristics, 2) the pattern of internet use, 3) diagnostic criteria of internet addiction among the students, 4) students' knowledge regarding internet addiction and 5) student's reported practices regarding internet addiction disorder. Results of this study showed; 42% of the students aged from 15 to less than 16 years old (X±SD = 15.62 ± 1.12). As regard birth order 79% were the youngest, 48% of them in the third year of the study, and 75% live in urban area. 75% of the students were having the accessibility to internet at home, and 65% of them use the Internet every free time per day. Total knowledge scores of the secondary schools students regarding internet addiction disorder were good for only31%, and the total practices scores regarding internet addiction were satisfactory for only 26% of the students. This study concluded that: The internet addiction has a high negative impact among the students. Also there were high statistically significant relation between socio demographic characteristics of the students and their knowledge and practices regarding internet addiction disorder. The study recommended that: A similar study can be replicated on a large sample and a comparative study can be done with students of different groups of adolescents.