"Be careful with love. Think twice before marrying a Muslim, think seriously because it brings loads of hassle - and even Allah can't say where all that will end,'' Jose Policarpo, the Cardinal Patriarch of Lisbon, said during a public debate.
"When you recognise what a young European of Christian upbringing is subjected to, given Muslim attitudes to women, the first time she goes to their countries, we can imagine what that entails.
"You can only dialogue with someone who is willing to dialogue. With our Muslim brothers, for example, dialogue is very difficult,'' he said.
"We have taken the first steps, but it's extremely difficult - because for them, their truth is the only way.''
Around 40,000 Muslims live in Portugal, according to Lisbon's Islamic community leaders - who have yet to react to the cardinal's remarks.
A spokesman for Portugal's episcopal community, Manuel Marujao, said that Policarpo was offering "realistic advice'' which he said amounted neither to "discrimination nor contempt for another culture or religion'', according to the Catholic news agency Ecclesia.