Buffett said in February he agreed to take the unusual step of selling Applied Underwriters because it's a smaller firm that competes against two larger insurance companies Berkshire owns that also sell workers' compensation coverage.
Terms of the deal weren't disclosed. Officials at Berkshire and Applied Underwriters didn't immediately respond to messages Wednesday.
Berkshire rarely sells or closes any of its companies because Buffett's preferred holding period is forever.
In the past, the only exception Buffett has made to this policy is for businesses that face the prospect of never-ending operating losses.