I've been on Tysabri for around 8 years now, and I've not noticed any hair loss. With that being said, I keep my hair very short (old military habits die hard) and it would be hard to notice it anyway :) I've not heard of hair loss as a possible side effect, but it very well could be for certain people. Based on your other post it sounds like Tysabri seems to be working, and that's wonderful. I was on REBIF while still recovering from the major relapse that led to my diagnosis when I had another relapse. My neurologist switched me over to Tysabri and I was able to quickly recover to my old self in only a few months (thankfully). I still deal with Lhermitte's sign, but its twinge varies day to day. I hope Tysabri continues to work for you.