Retail sales growth in Scotland has lagged behind the UK for more than a year, despite the recent sunny weather giving the high street a small boost.
Total sales for May were up 0.1% on the same month last year but like-for-like sales, which strip out factors such as new store openings, were down 1.2%, latest figures show.
The small rise in total sales was much lower than the UK as whole, which recorded 3.4% growth on May 2011, the 14th consecutive month in which UK sales growth beat that of Scotland.
Ian Shearer, director of the Scottish Retail Consortium (SRC), said: "A welcome spell of warmth at the end of May helped lift these figures but the burst of summer didn't bring a boost on the scale enjoyed elsewhere."
The "underlying picture remains weak, showing sales falling in real terms for the sector overall".
While total sales may have risen last month, it was still "particularly worrying given that they are being compared against poor figures for May in 2011" when sales dropped by 1.1%, he said.
Overall, the new figures show that "consumer caution persisted, household budgets are still under severe strain and most shoppers are committed to buying only what they consider to be essentials".
David McCorquodale, head of retail in Scotland for KPMG, said: "After a dismal April, May was a slightly better month statistically and many retailers will have breathed a small sigh of relief, particularly in the last week of May as the sun shone.
"However, closer scrutiny of the comparisons with last May doesn't make for comfortable analysis. Total sales rose only 0.1% against last May which itself recorded the worst fall we'd seen up to then."
The figures, contained in the latest Scottish Retail Consortium-KPMG retail sales monitor, show total food sales were up 3.8% and like-for-like sales were up 1.9%.