In this descriptive and correlational study, it was aimed to examine the relationship between adolescents' smartphone addiction and cyberchondria. Data were obtained from 384 adolescent high school students in Istanbul between December 2020 and January 2021, using a Personal Information Form, the Smartphone Addiction Scale, and Cyberchondria Severity Scale. The data were collected through face-to-face interviews with the students. The adolescents' smartphone use duration was 3.67 ± 1.66 years. Almost all (97.9%) connected to the internet via smartphones and 39.3% spent 3-4 h per day on the internet. It was determined that 61.7% of them checked their phones as soon as they woke up in the morning and 75.3% of them before going to bed in the evening. For those whose smartphone use duration is high, their cyberchondria also increases. The authors suggest that nurses should understand smartphone addiction and cyberchondria to identify and apply nursing interventions when necessary in adolescents.