UnitedHealth Group shares popped Friday after Berkshire Hathaway announced it purchased 5 million shares of the insurance giant.

Warren Buffett's Berkshire Hathaway increased its holdings in UnitedHealth Group stock, and also added positions in D.R. Horton, Lamar Advertising, and Nucor.

TheStreet. Warren Buffett is arguably the most successful investor of all time. He's amassed an amazingly massive net worth by buying and usually holding stocks for the long haul. Trained under legendary value fund investor Benjamin Graham,

UnitedHealth Group Inc. (NYSE:UNH) shares edged up on Monday, even as the stock remains down roughly 49% year to date. Trading volume stood at 6.39 million shares, well below the 100-day average of 20.

UnitedHealth Group ( UNH 12.04%) has been a solid dividend growth stock for years. Generally, its yield has been fairly low, due to the stock's rising value. Even as the healthcare insurance giant has grown its dividend, its yield hasn't been particularly high or noteworthy.

Year to date, the stock has fallen by nearly 45%, which is by no means normal for the healthcare stock. In fact, this is the worst it has performed since the Great Recession, when it tumbled by more than 54% in 2008.

Key Takeaways UnitedHealth Group shares surged Friday after Warren Buffett’s Berkshire Hathaway revealed a stake in the embattled healthcare giant.After bottoming at the start of August, the stock has continued to gain momentum,

Shares of some of UnitedHealth’s peers got a bump in the wake of Berkshire’s investment in the healthcare giant, and they all look cheaper based on price relative to expected earnings.

The company may be under criminal investigation for alleged irregularities in its Medicare business—but it’s been touched by the Warren Buffett effect. Shares in the troubled private health insurer UnitedHealth Group (NYSE: UNH) are currently seeing their best trading day in months.

U.S. equities were mixed at midday following the release of the July retail sales report, which came in as expected.