Banca Monte dei Paschi di Siena, the world's oldest surviving bank and Italy's third biggest, on Thursday reported a net loss for 2012 of 3.17 billion euros ($4.06 billion).
Of that sum, the ailing bank -- which has been caught up in a derivatives scandal -- registered a loss of 1.591 billion euros in the fourth semester alone, it said in a statement.
The bank, which benefited from a 4 billion euro rescue loan from the Italian government earlier this year, said it took 2.67 billion euros writedowns in 2012 to cover bad debts.
The bank said it operated "in an extraordinarily complex market environment characterised by a progressive slowdown in the economic growth and an exacerbation of the sovereign debt crisis in the eurozone."
The crisis "caused an abrupt increase in credit spreads and restricted access to interbank and institutional markets" making business conditions extremely difficult for the bank.
In January, Italian prosecutors launched legal proceedings against BMPS on reports it had lost some 700 million euros ($900 million) through risky investments in complex financial products.
The bank has said it will lay off 4,600 people by 2015 and close hundreds of branches.
BMPS posted a loss of 4.69 billion euros in 2011.