The chocolate maker reported sales figures for the 16 weeks to the end of 30 April this year.
Thorntons said that pre-tax profits for the year would range between £3m and £4.5m, compared to £6.1m the previous year.
This follows a warning in February that profits would be lower than expected.
Today's financial statement revealed that sales dropped 0.7% to £64.2m, compared to the previous 16 months.
The company's channel mix changed markedly, with sales through the company's retail operations falling 14.1% but sales through other retailers rising 25.1%.
Sales through Thortons' own stores plummeted in the Easter week period by an eye-watering 22.8% in comparison to the same period last year.
, Thorntons celebrated its 100th anniversary with an enlarged chocolate Easter range and tailored centenary products.
The company claimed, though, that through its promotions it has managed its seasonal stocks well and exited the Easter period with lower stock levels than last year.
Jonathan Hart, chief executive of Thortons, said: "The past quarter has been extremely challenging particularly in our own stores and for franchises and we foresee the prospect of this weakness in high-street footfall and spending continuing.
"We have taken a number of actions including adjusting our trading strategy and aggressively managing our overhead costs, as well as ensuring that our ice cream was available in more stores than last year ahead of the Easter trading period."
Thorntons operates 369 owned stores and 226 franchisee outlets.
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