The cause of death has not yet been determined, the police said on Tuesday. The man was arrested late on Monday afternoon.
A cleaner found the woman's body at the four-star Hotel Birger Jarl on Saturday afternoon. Hotel manager Marianne Hultberg told reporters that the cleaner had first thought the woman was asleep. The cleaner was later questioned by police officers and Hultberg said she was doing well considering the circumstances.
Police spent Saturday questioning other staff members and hotel guests and looking for forensic evidence at the hotel. The first floor was cordoned off and people entering the hotel were asked to confirm that they were guests.
Police have been restrictive with information about the victim and the incident, but the Aftonbladet tabloid cited sources that the body was found on the floor of the hotel room and that it had no visible sign of injuries.
Aftonbladet also claims there is CCTV footage of the suspect leaving the hotel four hours after the woman checked in at 4am on Saturday morning.