"It's so much work being a music director. You have to worry about everyone and everything - the musicians' salaries, the temperature on stage, the audience... you can't ease off and still do your job," he said. "I just want to be able to focus solely on the music."
Under his baton, the orchestra has grown from a 12-week season with 5,000 subscribers and a $5 million budget to a 37-week season with 35,000 subscribers and a $22 million budget.
Musicians' salaries have risen by 500 percent and the symphony has released more than 125 recordings, 11 nominated for Grammy Awards.
"If there's a time to get out, this is the time," Schwarz said.
One of his happiest achievements was construction of a glittering performance center, Benaroya Hall, which opened nearly 10 years ago on a once dingy and sketchy downtown hillside.
"What could be more exciting than to open a hall that made such a difference to the downtown area?" he said.
Susan Hutchison, symphony board president, said Schwarz's move had been "percolating for some time" before he told her in late June or early July that he was nearing a decision. He disclosed his plan late last month, and "I don't think it was a surprise," she said.
Even so, Hutchison said, "I think we all have this sense of 'Oh, dear.' It brings us to the end of an era."
Speight Jenkins, who celebrated his 25th anniversary as general director of the Seattle Opera in May, said he was happy that Schwarz plans to continue to live in Seattle and will conduct a new opera commissioned by the company, "Amelia" by Davon Hagen, in 2010.