Police spokesman Lars Bystrom says the woman was seriously injured in the crash in the early hours of Tuesday and was flown to a Stockholm hospital. No one else was injured.
Bystrom says she was arrested on suspicion of endangering the public.
Tomas Hedenius, a spokesman for train operator Arriva, says the woman, born in 1990, stole the four-car train at a depot outside Stockholm.
She then drove it about a mile (1.6 kilometers) to the end station on the railway line, where it jumped off the tracks and crashed into a three-story building. The motive was unclear.
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