structural:reformatting, structural:expansion
Illness and death

In spite of the emotional distractions, during the summer of 1910 Mahler worked on his Tenth Symphony, completing the Adagio and drafting four more movements. He and Alma returned to New York in late October 1910, where Mahler threw himself into a busy Philharmonic season of concerts and tours. Around Christmas 1910 he began suffering from a sore throat, which persisted. On 21 February 1911, with a temperature of 40 °C (104 °F), Mahler insisted on fulfilling an engagement at Carnegie Hall, with a program of mainly new Italian music, including the world premiere of Busoni's Berceuse élégiaque. This was Mahler's last concert. After weeks confined to bed he was diagnosed with bacterial endocarditis, a disease to which people with defective heart valves were particularly prone and which could be fatal. Mahler did not give up hope; he talked of resuming the concert season, and took a keen interest when one of Alma's compositions was sung at a public recital by the soprano Frances Alda, on 3 March. On 8 April the Mahler family and a permanent nurse left New York on board SS Amerika bound for Europe. They reached Paris ten days later, where Mahler entered a clinic at Neuilly, but there was no improvement; on 11 May he was taken by train to the Löw sanatorium in Vienna, where he developed pneumonia and slipped into a coma. Hundreds had come to the sanitorium during this brief period to show their admiration for the great composer. After receiving treatments of radium to reduce swelling on his legs and morphine for his general ailments, he died on 18 May.

On 22 May 1911 Mahler was buried in the Grinzing cemetery, as he had requested, next to his daughter Maria. His tombstone was inscribed only with his name because "any who come to look for me will know who I was and the rest don't need to know." Alma, on doctors' orders, was absent, but among the mourners at a relatively pomp-free funeral were Arnold Schoenberg (whose wreath described Mahler as "the holy Gustav Mahler"), Bruno Walter, Alfred Roller, the Secessionist painter Gustav Klimt, and representatives from many of the great European opera houses. The New York Times, reporting Mahler's death, called him "one of the towering musical figures of his day", but discussed his symphonies mainly in terms of their duration, incidentally exaggerating the length of the Second Symphony to "two hours and forty minutes". In London, The Times obituary said his conducting was "more accomplished than that of any man save Richter", and that his symphonies were "undoubtedly interesting in their union of modern orchestral richness with a melodic simplicity that often approached banality", though it was too early to judge their ultimate worth.

Alma Mahler survived her husband by more than 50 years, dying in 1964. She married Walter Gropius in 1915, divorced him five years later, and married the writer Franz Werfel in 1929. In 1940 she published a memoir of her years with Mahler, entitled Gustav Mahler: Memories and Letters. This account was criticised by later biographers as incomplete, selective and self-serving, and for providing a distorted picture of Mahler's life. The composer's daughter Anna Mahler became a well-known sculptor; she died in 1988. The International Gustav Mahler Society was founded in 1955 in Vienna, with Bruno Walter as its first president and Alma Mahler as an honorary member. The Society aims to create a complete critical edition of Mahler's works, and to commemorate all aspects of the composer's life.