The network was extended by new construction and by acquisition of the privately operated lines from Silkeborg to Herning (1 November 1879) and from Grenaa to Randers and Aarhus (1 April 1881).

New railway bridges were built across the Little Belt (1935), the Storstrøm (1937) and Oddesund (1938), eliminating the costly and time-consuming process of transfer by steam ferry.

World War II left DSB with a fleet of outdated and worn-out trains, and apart from a series of second-generation MO railcars and the class MT multi-purpose centercab engines built by Frichs, domestic industry was unable to provide the kind of motive power required.

However, this was also accompanied by the appearance of new technology, notably the utilisation of electronic equipment, improving the safety and efficiency of DSB's railway traffic.

In 1972, along with the celebration of the 125th anniversary of railways in Denmark, DSB introduced a new corporate design by architect Jens Nielsen, inspired by British Rail and Canadian National Railways, with red as the dominant colour (with engine rooms of locomotives painted black), replacing the traditional maroon livery with yellow winged wheel symbols.

Following the lead of the Nederlandse Spoorwegen, British Rail and Deutsche Bundesbahn, DSB in 1974 introduced a fixed interval timetable for its long-distance locomotive-hauled Intercity trains as well as the commuter services to and from Copenhagen.

The IC3 trains, being a specimen of the Flexliner type of multiple units, have a distinct appearance due to the rubber-framed ends, allowing access between trainsets when coupled together.

In 1997, infrastructural duties were branched off into a new agency under the Danish Ministry of Transport, Banestyrelsen (now: Banedanmark), leaving DSB with the task of train operation.

[5] In 2003, Arriva, in competition with DSB, won the tender for operating a number of regional railway services in Jutland: Tønder-Esbjerg, Esbjerg-Struer, Skjern-Aarhus, Struer-Langå-Aarhus and Struer-Thisted.

[9][10] Thus, DSB now operates on a for-profit basis, although it retains certain public service commitments via contracts with the Ministry of Transport and Energy.

In March 2015, the ongoing privatization process was put on hold until at least 2024, as part of a broad centre-left political majority agreement on passenger rail-transport.

Keld Sengeløv became president and CEO in February 2004, after a career in the DSB organization since 1997, but died from an undisclosed illness while travelling with friends in Scotland on 3 September 2006.