UnitedHealth Group's net income jumped 23 percent for the quarter that ended last month to $1.6 billion, up from $1.3 billion for the same period a year ago.
Enrollment in the health insurer's Medicare and Medicaid plans surged and medical costs stayed stable. Payments for health care consumed a smaller portion of revenue from premiums.
CEO Stephen Hemsley said revenue and profits will grow next year, too, but meeting Wall Street's expectations could be tough.
"We expect strong execution to continue in 2013," Hemsley said on a conference call with analysts Tuesday. "But as we have said, the weak business climate and employment outlook in the United States, the mounting pressures on federal and state budgets — to mention just a few of the challenges — we continue to be cautious."
Next month's presidential election also is creating uncertainty about the financial performance of health insurers. Republican presidential candidate Mitt Romney has promised to repeal President Barack Obama's massive health care overhaul.