BACKGROUND: Teens’ lifestyles have changed significantly during and after COVID-19 epidemic and they have started engaging in risky health behaviors like using smartphone more frequently. Everyone is compelled to use their smartphone more frequently than usual to access daily necessities during the COVID-19 pandemic lockdown. AIM: We aimed to evaluate the problem of internet addiction and the increasing use of smartphone among teenage Egyptian youth during COVID-19 pandemic. METHODS: Online surveys were sent to Egyptian teens (12–18 years old) in several governorates in June 2020, and they were completed by 154 youths over the course of one month. Different teenagers were required to respond to and share in this poll, and versions in both English and Arabic were used. At the outset of the questionnaire, the question about consent was viewed as mandatory. The extent of Internet use was evaluated using Young’s Internet Addiction Test (IAT). The survey was divided into four sections and created with the goals of understanding the modes (frequency, patterns, and goals) of internet use, the negative effects, linked parental behaviors, as well as the eventual occurrence and severity of addiction. The same data from the time before the epidemic was also looked into and analyzed. Version 23 of IBM SPSS Statistics was used for the analysis. The p-value threshold for significance was established at 0.05. RESULTS: The mean age of the teens was 14.38 ± 2.87 years and equal gender frequency (males of 50.6% and females of 49.4%. About 79.9% of them live in urban environment, 18.8% suffered from family problems and 40.9% were in the secondary educational level. Increased physical inactivity of participants was noticed after COVID-19 among participants (55.8%). About 87.7% of them used smartphone for online access (87.7%). Half of the subjects (50%) spent 1–3 h online before COVID, while more than half of them (59.1%) spent more than 6 hours online after COVID, with a statistically significant difference. Mean IAT was 61.91 ± 16.77 after COVID versus 45.26 ± 12.45 before COVID. The prevalence of internet addiction was increased from 67.5% before COVID-19 to 77.9% after COVID-19 infection. IAT score was normal, mild, moderate, and severe in 5.8%, 16.2%, 65.6%, and 12.3% after COVID-19, respectively, compared to normal, mild, moderate, and severe IAT score in 26.6%, 5.8%, 61.0%, and 6.5% before COVID, respectively, with significant differences between them before and after COVID (p < 0.000). Increasing mother’s and father’s educational, increasing time spent online, decreasing duration of sleep, and lower the number of days of exercise for more than 30 min/week were associated with higher IAT score. CONCLUSIONS: During the COVID-19 pandemic, internet addiction was extremely common among teenagers (77.9%). The amount of time spent online, the length of sleep, and the number of days that a person exercises for more than 30 min/week were all predictors of addiction.