The insurer Swiss Life warned on Wednesday that it would not reach its full-year profit goal because of market conditions and currency losses.
Switzerland's largest life insurer had earlier estimated it would achieve a net profit of between SFr1.8 billion ($1.5 billion) and SFr1.9 billion.
The news sent the share price tumbling, closing 20 per cent down at SFr87.15.
Swiss Life blamed the worsening of the global financial crisis since September, which has hit investments it made in hedge funds, stocks and companies that have since filed for bankruptcy.
"Along with the extraordinary gains of SFr1.5 billion from disposals, Swiss Life will report a clear loss on continuing operations for the 2008 financial year," the company said.
The Zurich-based firm said it would stop its share buyback program and freeze a proposed shareholder dividend payout of SFr600 million.
Swiss Life also said its subsidiary AWD, a financial services provider, would cut about 400 jobs in Britain and would sell its remortgaging business there.