RationaleThere has been growing concern that loneliness has increased throughout the COVID-19 lockdowns, and that the burden has fallen heavily on young people. This is important because loneliness is strongly linked to worse health outcomes. ObjectiveWe examine whether and how loneliness among young people changed during the pandemic across the different lockdown periods in 2020 and 2021. We also assess differences by gender, socioeconomic status, and economic activity before the COVID-19 outbreak. MethodsWe use nine waves of longitudinal data from the COVID-19 supplement of the UK Household Longitudinal Study (Understanding Society), collected between April 2020 and September 2021. We apply an individual fixed-effects event study design, which compares the loneliness reported by the same individual over lockdown transitions. We focus on loneliness reported by 1870 respondents aged between 16 and 24 years and compare it with pre-pandemic baselines. ResultsWe find that the loneliness of young people tracked the extent of lockdown restrictions but had returned to baseline levels by September 2021. This loneliness response was more pronounced for females than males but similar for young people across higher and lower socioeconomic backgrounds. ConclusionsThese results suggest that policy interventions aimed at increasing opportunities for in-person social interactions for young people in ‘normal’ times, might have some success in tackling loneliness, particularly for young females.