Hennes & Mauritz said like-for-like sales dropped by five per cent in March compared with the same month last year.
The fashion company said that the strong sales in March 2010 had been boosted by good Easter sales.
Total sales, which include new stores, were up two per cent.
Last month the Swedish chain said its first quarter profits had tumbled by 30 per cent, with higher cotton prices taking their toll.
from December to February, H&M said profits dropped to 2.62bn kronor (£258m), from 3.54bn kronor in the same period a year ago.