He was a patient at Praram 2 Hospital in Bangkok’s Bang Khunthian district.
Shortly before midnight hospital staff were alerted to a fire in a patient's room on the fourth floor of one of the hospital buildings.
Fire fighters were called and quickly extinguished the flames. Some patients were evacuated from the building but no one else was hurt.
Police said they found a male patient dead in bed with both feet and his left arm tied to the bed. He had burns to 90% of his body, with the worst injuries on his right side.
Peera Kunanuwat, director of Praram 2 Hospital, said the patient was admitted to the hospital for treatment of chronic tuberculosis and had been isolated from other patients to prevent the disease spreading through the air.
He had been treated at the hospital several times under the 30-baht national health scheme. The man was tied to the bed because he had previously tried to hurt himself.
Dr Peera said the patient asked for permission to smoke a cigarette around 9pm Sunday, but the nurse refused his request.
The police will investigate will review CCTV footage to establish the cause of the fire.