Introduction: This study investigates the stability of loneliness in adolescents over a 1-year period. Also, we examine how the use of screen time media (watching television, playing video games, surfing the Internet, and texting) predicts loneliness over a year and how loneliness predicts screen time media usage. Methods: The study uses survey data from the Cannabis, Obesity, Mental health, Physical activity, Alcohol, Smoking, and Sedentary behavior Study. A large (N = 20,903; 54% female) sample of Canadian students in grades 9-11 (Time 1) and grades 10-12 (Time 2) were assessed at two-time points, 1 year apart. Results: Loneliness scores were found to be stable over the 1-year period, with a slight increase. Additionally, while loneliness was associated with some screen time within the same year, the effects from loneliness or screen time variables at time one predicting the other at time two were negligible. The study also provides evidence that the various screen time media did not fit a single dimension. Finally, there were sex differences in loneliness and some of the media variables. Conclusions: Loneliness appears to increase slightly over the course of a year in high school students. Results indicated that Internet use and loneliness are related; however screen time use in one year does not have a substantial impact on loneliness a year later or vice versa. Lastly, the data suggested that researchers examine screen time behaviors individually in their investigations.