Food sales bucked the downward trend
Retail sales in May had their sharpest fall in nine years, according to the latest figures from the Scottish Retail Consortium.
The data showed that overall, sales fell 1.2% compared with the same month last year.
Sales of non-food items, such as clothes and furniture, were down by 5.7%.
Scottish shops appeared to be suffering more than those in the UK as a whole, where sales fell by 0.8% in May.
April's Scottish sales figures showed a strong rise of 4.3%, but Scottish Retail Consortium spokesman Richard Dodd said he believed that had been a blip.
Mr Dodd said: "Despite bank holidays and more sunshine in May neither the food nor non-food sectors have been able to maintain the consumer spending that was generated by Easter.
"But non-food retailing is having the toughest time as customers confine their spending to must-haves."
He said he believed talk of the green shoots of recovery was clearly premature despite food showing a 3.6% rise in sales, with the warmer weather giving a boost to barbecue products and salads.
However, the monthly food sales growth was still the lowest for at least a year.
Furniture and DIY continued to struggle during May with the weak housing market and consumer caution in the face of uncertain job prospects being blamed.
The Retail Monitor is produced monthly and compiled by the University of Edinburgh using data provided by a wide range of Scotland's shopkeepers.
It does not take into account business in new stores which have opened in the last year.
The research concluded that the depressed nature of sales was now entering its third year and that the extended period of low growth has imposed a heavy toll on small and medium-sized firms.
It said it expected the numbers of retailers still in business to have fallen considerably when official statistics become available.