Germany does not know the whereabouts of 130,000 asylum seekers who were registered last year, officials say.
The migrants did not appear at reception centres to which they had been directed, the government said in a written reply to a question.
This may be because they have moved to a different country, gone underground or registered several times.
Those missing represent about 13% of about 1.1 million asylum seekers registered in Germany in 2015.
A spokesman for the interior ministry said a series of measures approved by parliament on Thursday would help address the missing migrants problem, AFP news agency reports.
These include plans for them to receive an identity document on arriving in Germany so that the authorities can store personal data under a common database and avoid making repeated registrations.
The new rules also include measures to restrict family reunions for some migrants in addition to slackening the criteria used by the authorities to expel convicted foreigners.
This was a key measure put forward after New Year celebrations were marred when scores of women complained about being sexually assaulted and robbed by a crowd of predominantly migrant men.
Germany's main business associations are due to voice their concern over a potential collapse of the EU's border-free Schengen system at a meeting with Chancellor Angela Merkel on Friday in Munich.
They are expected to repeat their argument that migration can be a useful tool to replenish Germany's shrinking workforce.
On Thursday, the head of Germany's federal office for migration, Frank-Juergen Weise, said there were up to 400,000 people in the country whose identities were unknown to the authorities.
A special flight from Germany carrying 125 deported Afghans arrived in Kabul on Wednesday.
Afghans have become Germany's second largest group of asylum seekers, after Syrians, with 154,000 arriving in 2015.
Those arriving in Kabul all left voluntarily, German officials said.