Various symptoms have been reported to persist beyond the acute phase of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, which is referred to as long coronavirus disease 19 (long COVID-19). Over 65 million individuals suffer from long COVID-19. However, the causes of long COVID-19 are largely unknown. Since long COVID-19 symptoms are observed throughout the body, vascular endothelial dysfunction is a strong candidate explaining the induction of long COVID-19. The angiotensin-converting enzyme 2 (ACE2), the entry receptor for SARS-CoV-2, is ubiquitously expressed in endothelial cells. We previously found that the risk factors for atherosclerotic cardiovascular disease (ASCVD) and a history of ASCVD raise the risk of severe COVID-19, suggesting a contribution of pre-existing endothelial dysfunction to severe COVID-19. Here, we show a significant association of endothelial dysfunction with the development of long COVID-19 and show that biomarkers for endothelial dysfunction in patients with long COVID-19 are also crucial players in the development of ASCVD. We consider the influence of long COVID-19 on the development of chronic kidney disease (CKD) and ASCVD. Future assessments of the outcomes of long COVID-19 in patients resulting from therapeutic interventions that improve endothelial function may imply the significance of endothelial dysfunction in the development of long COVID-19.