Per Ditlev-Simonsen (born 12 June 1932) is a Norwegian politician. He was the mayor of Oslo, representing the Conservative Party, from 1995 to 2007. He stepped down on 23 August 2007 following the Swiss bank-account scandal.

Ditlev-Simonsen was an officer of the Norwegian Royal Guards, and he later attended Stanford University getting a Master of Arts degree. After college, Ditlev-Simonsen became a partner in his father's shipping company Sverre Ditlev-Simonsen & Co (SDS) in 1955. He was a partner in the company until 1995.

Ditlev-Simonsen was a Member of Parliament from 1981 to 1985, serving in the Standing Committee of Finance. From 1989 to 1990 Ditlev-Simonsen was Minister of Defence in the Cabinet of Jan P. Syse.

Ditlev-Simonsen was born in Oslo to ship owner Sverre Ditlev-Simonsen and Lily Kaurin. He was a grandson of Olaf Ditlev-Simonsen Sr, and nephew of Olaf Ditlev-Simonsen Jr. He was married to Benedicte Werring (d. 1990) from 1960, and to Turi Klaveness from 1992.^[1]

In August 2007, the presence of a hitherto unknown Swiss bank account was revealed. The revelation came after an acrimonious divorce involving his daughter, Cecilie Ditlev-Simonsen, the communications director of Norsk Hydro.^[2] The account, which contained NOK 1.5 million had been inherited by Ditlev-Simonsen after his wife died in 1990, and he eventually admitted to not having paid the Norwegian wealth tax on it.^[3]

The revelation caused several opposition politicians to call for Ditlev-Simonsen's resignation. Erna Solberg, the head of the Conservative Party, asked that Ditlev- Simonsen refrain from active campaigning for his party ahead of the local elections scheduled for 10 September. Even if he had not resigned, the 75 year old Ditlev-Simonsen was set to retire after the election.^[4] The incident was believed to be a cause of the Conservative's 4 percent drop in opinion polls, three weeks ahead of the election.^[5]