The aim of this longitudinal study was to investigate emerging adults’ mental health before and during the COVID-19 pandemic, and whether social support from mothers, fathers, and best friends moderated the change in mental health. Participants were 98 emerging adults (46% men) who were assessed prior to COVID-19 (Mage = 20.60 years) and during the first lockdown (Mage = 22.67 years). Results indicated that the pandemic did not uniformly lead to elevated levels of mental health problems, but instead depended on level of mental health problems prior to COVID-19 and the source of support. For emerging adults who already experienced more problems prior to COVID-19, more maternal support was related to decreases in general psychological distress and depressive symptoms, whereas more paternal support was related to increases in general psychological distress and depressive symptoms. Support from best friends were not associated with (changes in) mental health.All information about the content of the files is described in 'read me_van den Berg et al_2021.pdf'. This file also contains information about the recruitment, participants and data collection. Data and the syntax for the analyses as presented in the paper are also stored.