The number of visits to shops was down 2.7% in September 2013 compared to the same month a year before, the Scottish Retail Consortium said.
The numbers, which were described as "disappointing" by the shopping lobby, came days after other figures showed retail sales were down in the month, by 0.8% on a like-for-like basis from 12 months earlier.
Retailers had taken heart from positive figures over the hot summer but admit Scottish consumers are increasingly canny as disposable incomes remain tight.
Fiona Moriarty, the SRC director, said: "It's disappointing to see Scottish shopper numbers have dropped significantly after a solid result in August.
"While recent months have hinted at economic recovery, many of us are still cautious about making major purchases and may want to focus on managing budgets ahead of Christmas.
"We saw a similar story in last week's Scottish sales figures, which reported a slowdown after strong growth in the summer months."
The Scottish fall in footfall was worse than that for the whole of the UK, which was measured at 2.4%, year on year. Out-of-town shopping centres, however, did not fare so badly. Their UK footfall was only down 1.1%.
September tends to be a quieter month in the shops after the big rush to buy back-to-school clothes and supplies and take advantage of the last of the summer.
But this year's month on month drop was tough: footfall was down 5% in traditional High Streets and 2.1% in shopping centres across the UK.
Ms Moriarty hoped for boosts from seasonal clothes - September appears to have been especially tough for fashion and footwear - as the cold sets in. She said: "There's been better news in recent weeks, with signs that customers are responding well to autumn collections and thoughts are turning to the festive season."
Stephen Boyd, of the STUC, said historic falls in real incomes since the crash meant it was far from surprising that retail footfall and sales were both down last month.
"We are now in the 44th month of falling real incomes. The last time that happened was the 1870s," he said. "The debate on the labour market has recently been dominated by employment figures.
"Employment might be rising in Scotland - but, unfortunately, incomes are not.
"The reason the unemployment stats have never been as bad as we anticipated over the last few years is these massive falls in real wages.
"People have fixed costs they must meet before they can even think about shopping or luxuries. We have seen energy costs go up nearly 10% this week when wages have gone up 0.7% - before inflation - in the last year."
Asda, however, yesterday said discretionary income, the amount Scots can spend after life's essentials, was £1 a week higher than this time last year.
Scots have £161 of such discretionary income a week, that is £3 more than the UK average.
And Scotland is the only part of the UK where this figure is rising, the supermarket said, thanks to recent boosts in employment.
The SRC, meanwhile, also took another key measure of the health of the High Street: the vacancy rate. It said 10.1% of Scottish retail outlets were not trading in July of this year, just below the UK average.
Grim economics news isn't the only reason for the High Street crisis. The internet now accounts for 10.2% of sales, excluding fuel, according to the Office of National Statistics.