Hennes & Mauritz said like-for-like sales fell by 5% in March from the same month a yearearlier.
The Swedish firm said that the strong sales in March 2010 had been boosted by good Easter sales.
H&M said total sales - which include new stores - rose 2%.
Last month the fashion chain said its first quarter profits had fallen by 30%, blaming higher cotton prices and the value of the Swedish krona.
During December to February, H&M said profits dropped to 2.62bn kronor ($421m; £258m), from 3.54bn kronor in the same period a year ago.