The DM, which was introduced in West Germany in 1948 under Allied rule and adopted in East Germany in 1990, was replaced by the Euro in 2002.
On the 31st of December 2001, DM banknotes to the value of €76.57 billion were in circulation.
Since then, "more than 95% of DM banknotes in circulation have been exchanged" for Euros, Dorit Feldbrügge from the Bundesbank (German Central Bank) told The Local.
But that means that around five percent of the old currency is still lying around somewhere in people's homes or safes.
Notes and coins with a total value of 12.76 billion Marks, which equates to 6.53 billion Euros, were still in circulation at the end of June this year, according to statistics from the Bundesbank.
That's a massive 167.3 million notes and 23.5 billion coins which have still not been handed in.
So what has happened to the remaining five percent ?
Nostalgia appears to be the main reason for Germans holding onto their beloved D-Marks. Another explanation is that money collectors have added the out-of-date notes and coins to their collections, the Bundesbank believes.
It's possible that other notes and coins have simply been forgotten about, lost or destroyed.
The most popular bank note to hang onto is the ten-mark note, 72 million of which are still out there. The penny piece is the most treasured coin, with 9.7 billion of them still in circulation.
But it's not too late to cash in the old currency. Germans can exchange unlimited amounts of their old Deutschmarks for Euros at any time.
The huge amount of missing cash is slowly being turned in, at a rate of around 100 million DM per year, according to Der Spiegel.
But Germans aren't out of the ordinary in stashing away their former currency. The French, Italians and Spanish have also been reported to be somewhat tardy in exchanging their old cash.
But, while it is no longer possible to cash in old currency for euros in France and Italy - and the Spanish only have until the end of 2020 to complete their exchanges - there is no time limit in the Bundesrepublik.
Notes and coins issued after the June 20th 1948 can be exchanged at a rate of one euro for 1.95583 D-Marks.
The Bundesbank advises against sending the Deutschmarks to be exchanged by post, and instead suggests visiting one of their branches to complete the exchange.
With reporting by Verity Middleton