• Monarch – Margrethe II^[1]
• Prime minister – Anker Jørgensen

• 19 September – The 1978 electoral age referendum, leading to a lowering of the electoral age from 20 to 18 years.^[2]

Undated edit

• The death penalty is abolished for all crimes.^[3]

Badminton edit

• 13–15 April — With two gold medals, two silver medals and one bronze medal, Denmark finishes as the second best nation at the 6th European Badminton Championships in Preston, England.
• Gentofte BK wins Europe Cup.

Cycling edit

• Donald Allan (AUS) and Danny Clark (AUS) win the Six Days of Copenhagen six-day track cycling race.

Other edit

• 2 September — Ole Olsen wins the 1978 Individual Speedway World Championship at Wembley Stadium in London.

January–March edit

• 9 January — Christina Hembo, designer
• 20 January – Britt Raaby, freestyle swimmer
• 14 February – Rie Rasmussen, actress, film director, writer, model, and photographer
• 3 March – Nicolas Kiesa, racing driver
• 10 March – Kim Staal, Ice hockey player

April–June edit

• 3 April – Michael Gravgaard, football player
• 8 April – Christian Tafdrup, actor and filmmaker
• 22 April – Ida Auken, politician
• 26 April – Peter Madsen, footballer
• 30 April – Joachim Boldsen, handballer
• 13 May – Jeanette Varberg. historian and curator

July–September edit

• 5 July – Allan Simonsen, racing driver
• 12 July – Katrine Fruelund, handball player
• 22 July – Dennis Rommedahl, football player
• 24 July – Ole Yde, fashion designer

October–December edit

• 1 November – Lise Rønne, journalist and television presenter
• 23 November – Joachim Fischer Nielsen, badminton player
• 27 December – Jim Lyngvild, designer

• 1 March – Arne Sørensen, politician (born 1906)
• 18 March – Willy Hansen, cyclist (died 1906)
• 19 May – Carl Hansen, footballer (born 1898)
• 22 June – Jens Otto Krag, politician, former Danish prime minister (born 1914)

• 1978 in Danish television