Total sales in local currencies for the month were up 3% compared to March of last year, but comparable store sales - sales at stores and websites which have been in operation for a least a financial year - dropped 8%.
This compares with a 10% increase in comparable store sales in February, when total sales were up 24%.
The company said that severe weather conditions in some of its markets had hit trading. In a trading update released today, it said: "The late spring in combination with calendar effects have had a negative impact on sales in March".
H&M had 1,546 stores at March 31.