Listed second was unemployment, which was named by 26 percent of Americans, Gallup said.
Concern about the economy was 29 percent in September while unemployment was mentioned by 32 percent last month.
The federal budget deficit was third on Gallup's Most Important Problem list, at 12 percent, followed by dissatisfaction with government, 9 percent; healthcare, 7 percent, and "lack of money," 5 percent, the Princeton, N.J., polling agency said.
Other issues were named by less than 5 percent of Americans.
Democrats, independents and Republicans all became more likely to list the economy as the nation's top problem in October, Gallup said. The number of mentions was the most among Republicans, rising 14 percentage points, from 30 percent to 44 percent. Mentions of the economy by independents rose from 32 percent to 37 percent, and among Democrats from 26 percent to 33 percent.
Results are based on nationwide telephone interviews last Monday and Tuesday in the Gallup Daily tracking survey of 1,004 adults. The margin of error is 4 percentage points.