UnitedHealth Group reported on Thursday that it earned less than expected this past quarter, citing higher medical costs and pressure on its insurance division at a time when the company is still reeling from the shocking murder of a top executive last month.

Revenues for UnitedHealth Group amounted to $100.8 billion for the fourth quarter, below what analysts had predicted but still 6.8 percent higher than in the same quarter the year before. The company’s full-year revenue for 2024 rose to $400.3 billion. For UnitedHealthcare, the insurance division, full-year revenue increased to $298.2 billion, up 6 percent from 2023.

The results were the company’s first since Brian Thompson, the chief executive of UnitedHealthcare, was gunned down in front of a Midtown Manhattan hotel.

The murder unleashed public outrage aimed at big health insurers, over lack of access to health care and denials of coverage and insurance claims.

Some shareholders have urged UnitedHealth to issue a report on its practices that “limit or delay access to health care.”

Andrew Witty, UnitedHealth Group’s chief executive, said on a call with analysts on Thursday that frustrations about claims, including delays in receiving care and coverage, were “key areas for us to work hard at to improve.”

A successor to Mr. Thompson has not been named yet. Mr. Witty did not share details about filling the post, nor did he directly address the recent shareholder campaign.

But he and other executives discussed the loss of Mr. Thompson at the top of the call.

“He devoted his time to helping make the health system work better for all of the people we’re privileged to serve,” Mr. Witty said.

UnitedHealth’s results, which disappointed Wall Street, in many ways reflected broader trends and lingering issues for the industry. For several quarters, U.S. health insurers have taken hits to their earnings from high medical expenses and a tightening of government payment policies.

John Rex, the company’s chief financial officer, pointed to cutbacks in government rates in the payment system for Medicare Advantage program, the private insurance arm of the federal coverage for people 65 and over. UnitedHealth has substantial business in these Medicare private plans.

Medicare Advantage performance has declined throughout the industry recently, partly because of regulatory changes meant to prevent overcharging and following increased health spending among some older populations.

Mr. Witty also said there were costs associated with changes in Medicaid, the federal-state insurance program for the poor.

The company’s medical cost ratio, a measure of the cost of providing care, came in higher than expected in the most recent quarter, which could add fuel to investors’ concerns that increased costs for delivery of care might linger, said John Boylan, an analyst at Edward Jones, an investment firm.

UnitedHealth, however, kept its full-year guidance for 2025 intact, unaltered by recent pressure. Analysts at Morgan Stanley said in a research note that the company had set “reasonably prudent targets” for this year.

“Overall, our view is that United is well positioned to navigate the evolving health care landscape due to its diversified business model,” Mr. Boylan said.

UnitedHealth’s stock fell 6 percent on Thursday as investors digested the weaker-than-expected results. UnitedHealth’s results, often seen as a bellwether for performance across the industry, pushed down shares of its rivals, including CVS Health, which is the parent of the insurer Aetna.

UnitedHealth Group also owns Optum Rx, one of the country’s largest pharmacy benefit managers, which employers and government programs hire to oversee their prescription-drug benefits.

Optum Rx has faced scrutiny from regulators over concerns that it has raised drug prices, prioritizing its own interests above those of patients, employers and taxpayers. Just this week, the Federal Trade Commission released a report detailing how P.B.M.s could be inflating drug costs.

The agency criticized Optum Rx and two other major benefit managers — CVS Health’s Caremark and Cigna’s Express Scripts — for raising prices on generic drugs for cancer, heart disease and other illnesses as high as 1,000 percent of national average costs.

Mr. Witty, the UnitedHealth Group chief executive, defended Optum’s practices, stressing that 98 percent of the rebates were passed to customers. By 2028, he said, all rebates would be passed on. Drug prices in the United States, Mr. Witty argued, are “de novo set too high relative to any other price in the world,” and shifted the blame to drug companies.

“The P.B.M. acts on behalf of the ultimate payer — the employer, the union, the state,” Mr. Witty told analysts.

Mr. Witty did not address investigations by the Justice Department or lawsuits seeking to block its proposed acquisition of Amedsys, a large home care and hospice company.

Beyond rising medical costs and increasing use of health care services, UnitedHealth executives pointed to the widespread ransomware attack in 2024 that weighed on the company’s full-year profits. The cyberattack forced the shutdown of the company’s sprawling billing and payment system, Change Healthcare. The company has estimated that the data breach of health and privacy information affected more than 100 million people, and said this week that a review of personal information involved in the incident was “substantially complete.”

Luigi Mangione, 26, has been charged with multiple state and federal counts of murder as well as weapons and stalking offenses. He has pleaded not guilty.

UnitedHealth and the police have said that neither he nor his parents had medical insurance through UnitedHealth.