Roberts, who beat breast cancer five years ago, said in a blog post on the GMA website:
"I've been diagnosed with MDS or myelodysplastic syndrome. It's a disease of the blood and bone marrow and was once known as preleukemia.
My doctors tell me I'm going to beat this -- and I know it's true."
LINK: Read more of Robin's post on gma.yahoo.com.
Robin said her sister is an 'excellent match' and that greatly improves her chances.
Robin said she will continue to host Good Morning America until her transplant, at which point she will miss "a chunk of time."