structural:expansion
Later career and personal life

The timbre of Caruso's voice gradually darkened as he aged and by 1916, he began adding heroic tenor parts such as Samson, John of Leyden, and Eléazar to his repertoire. Caruso toured the South American nations of Argentina, Uruguay, and Brazil in 1917, and two years later performed in Mexico City. In 1920, he was paid the enormous sum of US$10,000 a night (US$ 152,000 in 2023) to sing in Havana, Cuba.

In 1917, the United States entered World War I, sending troops to Europe. Caruso did extensive charity work during the conflict, raising money for many war-related patriotic causes by giving concerts and participating enthusiastically in Liberty Bond drives. The tenor had shown himself to be a shrewd businessman since arriving in America. He put a sizable proportion of his earnings from record royalties and singing fees into a range of investments. Biographer Michael Scott writes that by the end of the war in 1918, Caruso's annual income tax bill amounted to $154,000 (US$ 3.12 million in 2023).

Prior to World War I, Caruso had been romantically linked to an Italian soprano, Ada Giachetti, who was a few years his senior. Though she was already married, Giachetti bore Caruso four sons during their liaison, which lasted from 1897 to 1908. Two survived infancy: Rodolfo Caruso (1898–1951) and singer/actor Enrico Caruso Jr. (1904–1987). Ada had left her husband, manufacturer Gino Botti, and an existing son to cohabit with the tenor. Information provided in Scott's biography of Caruso suggests that she was Caruso's vocal coach as well as his lover. Statements by Enrico Caruso Jr. in his book tend to substantiate this. Her relationship with Caruso broke down after 11 years and they separated. Giachetti's subsequent attempts to sue him for damages were dismissed by the courts.

In 1917, Caruso met and courted a 25-year-old socialite, Dorothy Park Benjamin (1893–1955). She was the daughter of Park Benjamin, a wealthy New York patent lawyer and author. In spite of the disapproval of Dorothy's father, the couple wed on 20 August 1918. They had a daughter, Gloria Caruso (1919–1999). Dorothy wrote two biographies of Caruso, published in 1928 and 1945. The books include many of Caruso's letters to his wife.

A fastidious dresser, Caruso took at least two baths a day and enjoyed good food and convivial company. He forged a particularly close bond with his Met and Covent Garden colleague Antonio Scotti – an amiable and stylish baritone from Naples. Caruso was superstitious and habitually carried several good-luck charms with him when he sang. He played cards for relaxation and sketched friends, other singers, and musicians. His wife, Dorothy, said that by the time she knew him, her husband's favourite hobby was compiling scrapbooks. He also amassed valuable collections of rare postage stamps, coins, watches and antique snuffboxes. Caruso was a heavy smoker of strong Egyptian cigarettes. This deleterious habit, combined with a lack of exercise and the punishing schedule of performances that Caruso willingly undertook season after season at the Met, may have contributed to the persistent ill-health which afflicted the last year of his life.