He was also insane during the 13 interviews the two psychiatrists held with them, a news conference heard.
Breivik admits carrying out the attacks but has pleaded not guilty to charges.
He has previously said the attacks were atrocious but "necessary", saying he was fighting to defend Europe from a Muslim invasion, which was being enabled by what he called "cultural Marxists" in Norway's Labour Party, and the European Union.
The two psychiatrists, in their report, concluded that he lived in his "own delusional universe where all his thoughts and acts are guided by his delusions".
The 243-page report will be reviewed by a panel from the Norwegian Board of Forensic Medicine.
Breivik, 32, is due to stand trial on 16 April for a hearing that would last 10 weeks.
It is unclear if the conclusions of the report - if approved by the panel - will prevent the trial from going ahead in its current form.
It will almost certainly mean that Breivik is detained into psychiatric care rather than receiving a lengthy jail term.
Before the report was made public, a lawyer for the victims said it did not matter what the conclusion was as long as Breivik was not allowed to go free.
"What will happen in the case, no matter what the conclusion, is that he (Breivik) will of course be incarcerated," John Christian Elden said.
"And if the outcome is criminally sane or insane, that is, first and foremost a psychiatric question. The most important thing in our clients' opinion is that he will not be able to walk the streets."