Mrs McCann said an ongoing review of the case by Scotland Yard and the release of a new age-progression picture of Madeleine had left them feeling "probably as positive" as they had been for a long time.
''We are realistic. We don't know what has happened but we know there is a very good chance that she could be alive - there is no evidence to the contrary,'' Mrs McCann said.
''We know year after year, missing children, children that have been abducted, are found alive.''
Her remarks come as the couple, from Rothley, Leicestershire, prepare to mark the anniversary of their daughter's disappearance tomorrow.
Mr McCann appealed for people to look at the new picture of Madeleine and get in touch with the police if they saw someone who resembled her.
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"There's a real possibility Madeleine is alive and if people have got information, evidence as to who took her or where Madeleine is or what has happened to her we want them to come forward.
"This is as good an opportunity as there has been at any time in the last five years," he said.