Purpose To examine implications of the COVID-19 pandemic on eating disorder (ED) features and psychopathology in female adolescents with anorexia nervosa (AN). Method In total 79 females with first-onset AN (aged 12–22 years) were included and were followed up across a period of 1 year. We assessed AN participants recruited pre-pandemic ( n  = 49) to those recruited peri-pandemic ( n  = 30). Pre- ( n  = 37) and peri-pandemic ( n  = 38) age-, and education-matched typically developing (TD) girls ( n  = 75) were used as a reference cohort. ED features and psychopathology were assessed at baseline. After 1 year of follow-up the association between pandemic timing and clinical course was assessed. Analyses of covariance were used to examine differences in ED features and psychopathology. Results Peri-pandemic AN participants experienced less ED symptoms at baseline compared to pre-pandemic AN participants. In particular, they were less dissatisfied with their body shape, and experienced less interpersonal insecurity. In addition, the peri-pandemic AN group met fewer DSM-IV criteria for comorbid disorders, especially anxiety disorders. In contrast, peri-pandemic AN participants had a smaller BMI increase over time. In TD girls, there were no differences at baseline in ED features and psychopathology between the pre- and peri-pandemic group. Conclusion Overall, peri-pandemic AN participants were less severely ill, compared to pre-pandemic AN participants, which may be explained by less social pressure and peer contact, and a more protective parenting style during the pandemic. Conversely, peri-pandemic AN participants had a less favorable clinical course, which may be explained by reduced access to health care facilities during the pandemic. Level of evidence Level III: Evidence obtained from well-designed cohort or case–control analytic studies.