In recent months, the new coronavirus SARS-CoV-2 has emerged as a worldwide threat with about 4.2 million confirmed cases and almost 300 000 deaths. Its major clinical presentation is characterized by respiratory symptoms ranging from mild cough to serve pneumonia with fever and potentially even death. Until today, there is no known medication to improve clinical symptoms or even prevent or fight the infection. The search for a useful vaccination is ongoing and it will probably not be available before the end of 2020. In this review, we highlight hydroxychloroquine (HCQ) as a potential agent to prevent coronavirus disease 2019 (COVID-19) and reduce as well as shorten clinical symptoms. Moreover, it might serve as a potential post-exposition prophylaxis. Although it has been used in the treatment of rheumatoid arthritis, discoid or systemic lupus erythematosus, and malaria prophylaxis and therapy for decades, knowledge on HCQ as a potential treatment for COVID-19 is limited and multiple clinical trials have just emerged. Especially, rare HCQ side effects which were of minor importance for use in selected indications might gain major relevance with population-wide application. These rare side effects include retinopathy and-even more important-QT prolongation leading to sudden cardiac death by malignant arrhythmias.