In May 2000, Stewart was diagnosed with thyroid cancer, for which he underwent surgery in the same month. It had been previously reported he suffered from a benign vocal cord nodule. Besides being a major health scare, the resulting surgery also threatened his voice, and he had to re-learn how to sing. Since then he has been active in raising funds for The City of Hope Foundation charity to find cures for all forms of cancer, especially those affecting children.
Before returning to the UK, Stewart played for his LA Exiles team made up of mostly English expatriates plus a few celebrities, including Billy Duffy of The Cult, in a senior soccer league in Palos Verdes, California.
Despite his father being a supporter of Hibernian, Stewart is a supporter of Celtic, which he mentions in “You’re in My Heart”. He supports the Scotland national team and follows Manchester United as his English side, and he explains his love affair with both Celtic and Manchester United in Frank Worrall’s book, Celtic United. Stewart clarifies this more in his 2012 book (pp 163–64), Rod: The Autobiography, mentioning he “only had an attachment to Manchester United in the 1970s, but that was because they had so many great Scottish players in the 1970s, including Denis Law … When I did eventually click with a team, it was Celtic”. He presented Celtic with the trophy after they won the 2015 Scottish League Cup Final.
Stewart is a model railway enthusiast. His 23 x 124 foot (≈7 x 37 m) HO scale layout in his Los Angeles home is modelled after the New York Central and the Pennsylvania Railroads during the 1940s. Called the Three Rivers City, the layout was featured in the cover story of the December 2007, December 2010, and February 2014 issues of Model Railroader magazine. In the 2007 article, Stewart said that it meant more to him to be in a model railroad magazine than a music magazine. He has a second layout at his UK home, based on Britain’s East Coast Main Line. In a sidebar to the 2014 Model Railroader article, Stewart admitted (in an anecdote about his having unwittingly mixed red scenery texturing material into a “turf” mix he used around the bases of buildings) that he is colour-blind.
An auto collector, Stewart owns one of the 400 Ferrari Enzos. In 1982, Stewart was car-jacked on Los Angeles’ Sunset Boulevard, while he was parking his $50,000 Porsche. The car was subsequently recovered. – Wikipedia