A $24 Billion Dynasty’s Swiss Firm Gives Surprise Peek at Stocks

One of the most sophisticated investment firms for the world’s rich is opening up — just a little bit.

Longbow Finance, a Swiss family office that’s catered to the $24 billion Rausing dynasty for the past six decades, revealed for the first time its ownership of US equities in a recent regulatory filing. The portfolio — 57 stocks valued at $742.4 million — mostly comprised tech, health care and consumer shares at the end of last year, with Microsoft Corp. as its biggest position.

While US equities account for only a fraction of Longbow’s assets — which also include hedge funds, private ...