BACKGROUND: Corona contact tracing apps are a novel and promising measure to reduce the spread of COVID-19. They can help to balance the need to maintain normal life and economic activities as much as possible while still avoiding exponentially growing case numbers. However, a majority of citizens needs to be willing to install such an app for it to be effective. Hence, knowledge about drivers for app-uptake is crucial. OBJECTIVE: The present study aims to add to our understanding of underlying psychological factors motivating app-uptake. More specifically, we investigated the role of concern for one's own health and concern to unknowingly infect others. METHODS: A two-wave survey with N = 346 German-speaking participants from Switzerland and Germany was conducted. We measured the uptake of two decentralized contact tracing apps officially launched by governments ("Corona-Warn-App", Germany; "SwissCovid", Switzerland) as well as concerns regarding COVID-19 and control variables. RESULTS: While controlling for demographic variables as well as general attitudes towards the government and the pandemic, logistic regression analysis showed a significant effect of self-focused concerns (Odds Ratio = 1.64, P <.01). Meanwhile, concern to unknowingly infect others did not contribute significantly to the prediction of app-uptake over and above concern for one's own health (Odds Ratio = 1.01, P = .92). Longitudinal analyses replicated this pattern and showed no support for the possibility that app-uptake provokes changes in levels of concern. Testing for a curvilinear relationship, no evidence was found that "too much" concern leads to defensive reactions and reduces app-uptake. CONCLUSIONS: As one of the first studies to assess the installation of already launched corona tracing apps, our study extends our knowledge of the motivational landscape of app-uptake. Based on that, practical implications for communication strategies and app design are discussed. CLINICALTRIAL: