Mexico's President Enrique Peña Nieto filled about 30 percent of his undergraduate law thesis with unattributed paragraphs lifted from books, according to a report.
Published late on Sunday on the website of journalist Carmen Aristegui, the report found that 197 paragraphs of the 682 in Peña Nieto's thesis bear a remarkable similarity to the work of 10 authors.
It contains examples of how the young Peña Nieto apparently copied some of these word for word in his 1991 thesis.
The report highlights 20 paragraphs almost identical to ones contained in a book written by former President Miguel de la Madrid, who it claims is not mentioned anywhere in the 200-page text, or included in the bibliography.
Presidential spokesman Eduardo Sánchez moved quickly to dismiss the plagiarism allegation and question whether 'errors of style' from a generation ago should hold any interest for the public today.
"It appears that errors of style, such as quotes without quotation marks or the lack of references to authors contained in the bibliography, are matters of journalistic interest, two and a half decades later," Sánchez said in a statement he relayed via Twitter late on Sunday.
This is not the first time that Aristegui's investigative teams has made the president uncomfortable.
The team triggered a major conflict of interest scandal with its November 2014 report revealing the existence of a modernist mansion — dubbed the White House — which was designed and built for the president's family by a favored government contractor. Aristegui would also later allege that presidencial pressure was behind her subsequent dismissal from her popular morning news show on MVS Radio.
The presidency denied all involvement in Aristegui's removal, just as it has always refuted any wrongdoing regarding the White House.
The scandal has rumbled on nonetheless, with President Peña Nieto seeking to bury it forever in July this year when he made a highly unusual apology for handling the issue in a way that had "damaged the institution of the presidency."
The latest report questioning presidential credibility comes at a time when Peña Nieto's approval ratings have plummeted to just 23 percent, according to a poll published by the newspaper Reforma earlier this month.
Follow Jo Tuckman on Twitter: @jotuckman