structural:expansion
Denials of authenticity and legal action

After the diary became widely known in the late 1950s, various allegations against the veracity of the diary and its contents appeared, with the earliest published criticisms occurring in Sweden and Norway. In 1957, Fria ord ("Free Words"), the magazine of the Swedish neofascist organization National League of Sweden, published an article by Danish author and critic Harald Nielsen, who had previously written antisemitic articles about the Danish-Jewish author Georg Brandes. Among other things, the article claimed that the diary had been written by Meyer Levin.

In 1958, at a performance of The Diary of Anne Frank in Vienna, Simon Wiesenthal was challenged by a group of protesters who asserted that Anne Frank had never existed, and who challenged Wiesenthal to prove her existence by finding the man who had arrested her. Wiesenthal indeed began searching for Karl Silberbauer and found him in 1963. When interviewed, Silberbauer admitted his role and identified Anne Frank from a photograph as one of the people arrested. Silberbauer provided a full account of events, even recalling emptying a briefcase full of papers onto the floor. His statement corroborated the version of events that had previously been presented by witnesses such as Otto Frank.

In 1959, Otto Frank took legal action in Lübeck against Lothar Stielau, a school teacher and former Hitler Youth member who published a school paper that described the diary as "a forgery". The complaint was extended to include Heinrich Buddegerg, who wrote a letter in support of Stielau, which was published in a Lübeck newspaper. The court examined the diary in 1960 and authenticated the handwriting as matching that in letters known to have been written by Anne Frank. They declared the diary to be genuine. Stielau recanted his earlier statement, and Otto Frank did not pursue the case any further.

In 1976, Otto Frank took action against Heinz Roth of Frankfurt, who published pamphlets stating that the diary was "a forgery". The judge ruled that if Roth were to publish any further statements he would be subjected to a fine of 500,000 German marks and a six-month jail sentence. Roth appealed against the court's decision. He died in 1978, and after a year his appeal was rejected.

Otto Frank mounted a lawsuit in 1976 against Ernst Römer, who distributed a pamphlet titled "The Diary of Anne Frank, Bestseller, A Lie". When a man named Edgar Geiss distributed the same pamphlet in the courtroom, he too was prosecuted. Römer was fined 1,500 Deutschmarks, and Geiss was sentenced to six months imprisonment. The sentence of Geiss was reduced on appeal, and the case was eventually dropped following a subsequent appeal because the time limit for filing a libel case had expired.

With Otto Frank's death in 1980, the original diary, including letters and loose sheets, was willed to the Dutch Institute for War Documentation, which commissioned a forensic study of the diary through the Netherlands Ministry of Justice in 1986. They examined the handwriting against known examples and found that they matched. They determined that paper, glue, and ink were readily available during the time the diary was said to have been written. They concluded that the diary was authentic, and their findings were published in what has become known as the "Critical Edition" of the diary. In 1990, the Hamburg Regional Court confirmed the diary's authenticity.

In 1991, Holocaust deniers Robert Faurisson and Siegfried Verbeke produced a booklet titled " The Diary of Anne Frank: A Critical Approach ", in which they revived the allegation that Otto Frank wrote the diary. Purported evidence, as before, included several contradictions in the diary, that the prose style and handwriting were not those of a teenager, and that hiding in the Achterhuis would have been impossible. In 1993, the Anne Frank House in Amsterdam and the Anne Frank Fonds in Basel filed a civil lawsuit to prohibit further distribution of Faurisson and Verbeke's booklet in the Netherlands. In 1998, the Amsterdam District Court ruled in favour of the claimants, forbade any further denial of the authenticity of the diary and unsolicited distribution of publications to that effect, and imposed a penalty of 25,000 guilders per infringement.