The Grand Hotel and the nearby Brighton Centre was evacuated on Sunday following a bomb scare.
The hotel received an anonymous phone call at 4.30pm on Sunday 10 September, with the caller saying that an explosive device had been planted.
The hotel was evacuated and roads around the hotel were closed for almost five hours while specialists conducted a search.
Sussex police said that nothing was found and the call was being treated as a hoax.
Chief superintendent Lisa Bell of Sussex police said: “It was important that this report was thoroughly looked into, and we are grateful for the patience and understanding of staff, guests, and people using the nearby car parks, whose afternoon and evening was disrupted.
“A comprehensive criminal investigation is underway to trace the person responsible for the call. We are not disclosing any details of the call, but certain lines of enquiry are being actively followed.”