R-T, Margaret, and the Rats of NIMH is a 1990 children's book by Jane Leslie Conly with illustrations by Leonard Lubin.

When two children, Margaret and her younger, autistic[1] brother Artie ("R-T"), are lost during a camping trip, they are found by the colony of rats, specifically one named Christopher.

The children help the rat community with various tasks, and Artie and Christopher become very close friends.

The children try to keep the secret of Thorn Valley, but after pressure, Margaret ends up revealing it.

The whereabouts and fate of the rats of NIMH are left unstated, though Artie does find a gift from Christopher, a picture of an arrow, presumably pointing to the new location of the colony.