BackgroundAdolescent solitude was drastically impacted by the COVID-19 pandemic. As solitude is crucial for adolescent development through its association with both positive and negative developmental outcomes, it is critical to understand how adolescents’ daily-life solitary experiences changed as a result of the pandemic.MethodsUsing three waves of Experience Sampling Method data from a longitudinal study, we compared adolescents’ daily-life solitary experiences in the early (nT1=100; MAge=16.1; SDAge=1.9; 93% girls) and mid-pandemic (nT2=204; MAge=16.5; SDAge=2.0; 79% girls) to their pre-pandemic experiences.ResultsWe found that adolescents with lower levels of pre-pandemic social support and social skills reported wanting to be alone less and feeling like an outsider more at both time points during the pandemic. In the mid-pandemic wave, adolescents with higher levels of pre-pandemic social support and social skills reported decreases in positive affect compared to the pre-pandemic wave.ConclusionThis study shows that adolescents’ daily-life solitary experiences worsened throughout the COVID-19 pandemic. There should be continued concern for the wellbeing of all adolescents, not only those already at risk, as effects of the pandemic on mental health might only manifest later.