The Rennsteiglauf (full name GutsMuths-Rennsteiglauf) is a trail running event on the Rennsteig path in the Thuringian Forest.
The longest course is a ultramarathon currently 72.7 km from Eisenach to Schmiedefeld and part of the European Ultramarathon Cup. Other competitions are a marathon (43.5 km) from Neuhaus am Rennweg to Schmiedefeld, a half marathon from Oberhof to Schmiedefeld, short cross country races for people with intellectual disabilities and several hiking courses from 10 to 50 km.
Since 1973, the race has taken place annually in May. It used to be the biggest popular sport event in East Germany, and is still one of the biggest ultramarathons in Europe, attracting more than 10,000 participants, including those for other distances. It was named in honor of sports educator Johann Christoph Friedrich GutsMuths.