Europe's biggest insurer ING has stunned investors with a net loss of 9.6bn euro (£6.5bn) for 2002 after reporting its results under US accounting rules.
Two sets of accounts are now required
The figure includes a 13.1bn euro writedown, reflecting a massive fall in the value of recently acquired assets.
The company claims it has been the victim of tough new US accountancy rules introduced in the wake of the Enron scandal.
But analysts said the size of the goodwill charge called into question the profitability of parts of its business.
Goodwill is an accounting method used to represent the value of intangible assets such as brand or customer base.
ING dismissed the writedown as an "accountancy charge".
But that did not prevent ING shares taking a hammering following the announcement, trading down 6.4% at 10.93 euros.
The insurance industry has been under the cosh in recent months, as falling stock markets wipe billions off the value of cash reserves.
But some investors were puzzled as to why ING had left the goodwill charge out of its annual results, which it posted last month.
A company spokeswoman said it had always produced two sets of figures, as it is listed on the Amsterdam and New York stock exchange, which have different accountancy standards.
The discrepancy was particularly high this year, she conceded, because ING had overpaid for businesses in the US.
But, she added, it was also the first time the company has been forced to calculate its goodwill under tougher new US regulations for the first time.
In future years the discrepancy "would be nowhere near the same level", she added.
ING was unable to say which parts of its business had been affected by the writedown.