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.

Even though Warren Buffett seems to think the value of UnitedHealth stock is about right, that doesn’t mean investors should ignore the long list of unresolved issues facing the company.

Berkshire Hathaway's latest regulatory filing revealed that the company took a considerable stake in UnitedHealth. The 5 million-share, $1.6 billion stake makes the massive health insurer the 18th-biggest position in Berkshire's portfolio. Buffett's company also trimmed its positions in Apple and Bank of America.