Researchers at the US Department of Energy's Argonne National Laboratory in Illinois said bone fragments from Beethoven's skull, tested at the country's most powerful X-ray facility, had high concentrations of lead, matching an earlier finding of lead in his hair.
"The finding of elevated lead in Beethoven's skull, along with DNA results indicating authenticity of the bone/hair relics, provides solid evidence that Beethoven suffered from a toxic overload of lead," said Bill Walsh, director of the Beethoven Research Project, in a statement.
"There is no doubt in my mind ... he was a victim of lead poisoning," Mr Walsh said.
Beethoven, whose piano, chamber and symphonic works count as some of the greatest of Western classical music, died at 56 in 1827 after years of struggling with unknown ailments, including progressive deafness in his later years.
He had begun suffering from abdominal pains at 20 which became more aggravated throughout his life, and the composer saw a large number of physicians in search of a cure.
The description of his symptoms and the results of an autopsy shortly after his death are also consistent with lead poisoning, Mr Walsh said.
"Beethoven suffered from bad digestion, chronic abdominal pain,
irritability and depression," said Mr Walsh, a medical toxicologist at the Pfeiffer Treatment Center in Warrenville, Illinois.
Mr Walsh also said that it was possible that lead poisoning caused Beethoven's deafness.
The tests on the composer's bone fragments were made at the laboratory's Advanced Photon Source, an 800 meter (half-mile) particle accelerator which can fire intense X-ray beams 100 times brighter than the surface of the sun.
By directing the X-rays through the bone fragments, the scientists could measure the presence of key elements, without destroying the bones.
The results showed no detectable levels of either cadmium or mercury, the scientists said, which were previously thought to be possible causes of Beethoven's illnesses.
However, lead levels were pronounced, and half-life measurements of the lead suggest it was present in Beethoven's body for many years, according to the scientists.
The source of the lead is unknown, but they said some people speculate that Beethoven drank a respectable amount of wine, and the lead may have come from a wine goblet made with the metal.
Alternatively, some medical treatments in the 18th and 19th centuries made use of heavy metals like lead and mercury.
The fragments of Beethoven's skull are owned by California businessman Paul Kaufman, who inherited them from his great uncle, an Austrian doctor, who got them in 1863 during an exhumation of Beethoven's body.