The policy, spelled out in a guide for laymen and posted on the Vatican's website, matches the policy worked out by US bishops after an explosion of sex abuse cases in 2002.
Unlike the American norms, however, the Vatican guide contains no call for "zero tolerance" for priests who rape and molest children, and victims immediately criticised it as insufficient.
The Vatican insists it has long been the Catholic Church's policy for bishops, like all Christians, to obey civil reporting laws. But such an explicit policy had never been spelled out - until Monday.
"Civil law concerning reporting of crimes to the appropriate authorities should always be followed," said the newly posted guideline.
That phrase was not included in a draft of the document obtained on Friday by The Associated Press.
The Vatican offered no explanation for the addition. However, Pope Benedict XVI has come under increasing pressure to show the Vatican is serious about confronting clerical abuse and cracking down on church officials who let it go on virtually unchecked for decades.
The Reverend Thomas Reese, a Vatican analyst, said the guidelines will help parishioners hold bishops accountable.
"While the Vatican never told bishops they could not report abuse to the police, this is the first time the Vatican has been so clear on the responsibility to follow civil law concerning reporting of crimes," said Reese, a Jesuit priest and senior fellow at the Woodstock Theological Centre at Georgetown University.
Still, it was unclear what enforcement mechanism the guideline published on Monday might have. It is just that - a guideline - and not an official instruction to bishops from the Congregation for the Doctrine of the Faith.
In addition, the guideline makes clear that bishops are to report "crimes" - not just allegations.
Victims were not impressed by Monday's action.
"Let's keep this in perspective: It's one sentence and it's virtually nothing unless and until we see tangible signs that bishops are responding," said Joelle Casteix, western regional director for SNAP, the Survivors Network for Those Abused by Priests, the main victims' group in the US.
"One sentence can't immediately reverse centuries of self-serving secrecy."
She said if the Vatican truly wanted to change course "it would be far more effective to fire or demote bishops who have clearly endangered kids and enabled abuse and hid crimes, than to add one sentence to a policy that is rarely followed with consistency".
The document falls far short of US norms. That policy, approved by the Vatican as church law in the US, bars credibly accused priests from any public church work while the allegations are investigated.
Diocesan review boards, comprised mostly of lay people, help bishops oversee cases. Clergy found guilty are permanently barred from public ministry and, in some cases, ousted from the priesthood.