The catastrophic Vallascia avalanche struck the village of Airolo in the southern Swiss Alps on 12 February 1951. The accident was one of the most severe disasters during the catastrophic avalanche cycle of winter 1951. Shortly afterwards, one of the largest avalanche defense projects in Switzerland was initiated to prevent further catastrophic avalanches. In approx. 60% of the potential release area supporting structures were built. In 2016 the existing hazard map was re-evaluated in view of the extensive mitigation measures. The well documented 1951 avalanche allowed a comprehensive back-analysis. We determined the reduced hazard zones based mainly on the avalanche history, simulations with the 2D dynamics model RAMMS and expert judgment. A special focus was put on assessing the effectiveness of the mitigation measures. Calculating the runout area was not straightforward since several rows of houses brake the avalanche flow. The case study of Airolo is well suited to demonstrate the different facets and the complexity of such an analysis.