diff --git a/README.md b/README.md
index 118fe71d3e..6309385df2 100644
--- a/README.md
+++ b/README.md
@@ -17,6 +17,8 @@ need to build OpenSim before running it.
 
 # Running OpenSim on Windows
 
+You will need .NET Framework 3.5 installed to run OpenSimulator.
+
 We recommend that you run OpenSim from a command prompt on Windows in order
 to capture any errors.