Mozart’s final illness and death are difficult topics of scholarship, obscured by romantic legends and replete with conflicting theories. Scholars disagree about the course of decline in Mozart’s health—particularly at what point Mozart became aware of his impending death and whether this awareness influenced his final works. The romantic view holds that Mozart declined gradually and that his outlook and compositions paralleled this decline. In opposition to this, some contemporary scholarship points out correspondence from Mozart’s final year indicating that he was in good cheer, as well as evidence that Mozart’s death was sudden and a shock to his family and friends. The actual cause of Mozart’s death is also a matter of conjecture. His death record listed “hitziges Frieselfieber” (”severe miliary fever”), a description that does not suffice to identify the cause as it would be diagnosed in modern medicine. Dozens of theories have been proposed, including trichinosis, mercury poisoning, and rheumatic fever. The contemporary practice of bleeding medical patients is also cited as a contributing cause.

Mozart died around 1 a.m. on December 5, 1791 in Vienna, while he was working on his final composition, the Requiem. A younger composer, and Mozart’s only pupil at the time Franz Xaver Süssmayr, was engaged by Constanze to complete the Requiem. He was not the only composer asked to complete the Requiem but is associated with it over others due to his significant contribution.

According to popular legend, Mozart was penniless and forgotten when he died, and was buried in a pauper’s grave. In fact, though he was no longer as fashionable in Vienna as before, he continued to have a well-paid job at court and receive substantial commissions from more distant parts of Europe, Prague in particular. Many of his begging letters survive but they are evidence not so much of poverty as of his habit of spending more than he earned. He was not buried in a “mass grave” but in a regular communal grave according to the 1784 laws. Though the original grave in the St. Marx cemetery was lost, memorial gravestones (or cenotaphs) have been placed there and in the Zentralfriedhof. In 2005, new DNA testing was performed by Austria’s University of Innsbruck and the US Armed Forces DNA Identification Laboratory in Rockville, Maryland to determine if a skull in an Austrian Museum was actually his, using DNA samples from the marked graves of his grandmother and Mozart’s niece. However, test results were inconclusive, showing that none of the DNA samples were related to each other.

In 1809, Constanze married Danish diplomat Georg Nikolaus von Nissen (1761-1826). Being a fanatical admirer of Mozart, he edited vulgar passages out of many of the composer’s letters and wrote a Mozart biography.