[3] Diepgens tenure also saw the glamorous celebrations for the city's 750th anniversary, with visits from Queen Elizabeth II and US President Ronald Reagan.

[5] In late 1988, Diepgen called a state election on relatively short notice, hoping to capitalize on his personal popularity and to pre-empt an assault on the Christian Democrats over local problems such as a housing shortage and unpopular national policies, including proposed changes in the health service.

The first state elections of the united Berlin took place on 2 December 1990[8] and resulted in the CDU reasserting itself as the strongest party with 40.3 percent of the vote.

[9] Diepgen immediately initiated the relocation of the seat of the governing mayor and the Senate Chancellery from Schöneberg to Berlin's town hall in the Mitte district.

Also in 1991, Diepgen ordered the removal of a 3.5-tonne sculpture of Lenin, wanting to rid the city of an icon of a "dictatorship where people were persecuted and murdered.

[14] Amid the revelations of the CDU donations scandal in early 2000, Diepgen opposed Angela Merkel as new chairwoman of the party.

[15] On 6 July 2000, Diepgen signed a treaty with Matheus Shikongo, the Mayor of Windhoek, on a twin city partnership between the two municipalities.

[27] In 1986, Diepgen acknowledged accepting 50,000 West German marks, or about $21,000, from real estate investor Kurt Franke without having reported the amount as a party contribution as demanded by law.

[29] At the funeral of actress Marlene Dietrich in 1992, a simple graveside service at Städtischer Friedhof III, Diepgen was booed by Berliners who had been angered and disappointed by the city's failure to mount a formal tribute.

[31] He had backed a plan for a far smaller stone memorial inscribed simply with the words Thou Shalt not Kill proposed by theologian Richard Schröder, saying that its precision, dignity and modesty gave it more power than Peter Eisenman's project.