New ISD Scotland statistics show 14.5 per cent of patients attending A&E departments in November waited more than four hours.
The targets for patients to be admitted, transferred or discharged within four hours has only been missed by a greater margin once since 2007, according to the official figures.
There were 141,868 attendances to A&E departments across Scotland during November 2018, with 85.5 per cent seen in the required time.
A total of 3,320 patients had to wait more than eight hours in an A&E department, while 987 spent more than 12 hours waiting for treatment.
The only time a lower proportion of patients were seen within the target time – set in 2007 by the Scottish Government – was in December 2017 when it dropped to 85.1 per cent.
Compared to November 2018, there has been a 5.8 per cent drop in instances where A&E departments have met the target, which has not been hit since August 2017.
The worst-performing Scottish health board was NHS Lothian, where 81.4 per cent of patients were seen within the target period, followed by NHS Greater Glasgow and Clyde (81.8 per cent) and NHS Ayrshire and Arran (82.2 per cent).
In the Western Isles, 99.4 per cent of patients were admitted to hospital, transferred or discharged within the four hours – the only health board above the 98 per cent figure previously considered the “standard” for A&E waiting times.
A Scottish Government spokeswoman said: “Scotland’s core A&E departments continue to be the best-performing in the UK and have been for more than four-and-a-half years despite experiencing continued high attendance levels.”
Scottish Conservative health spokesman Miles Briggs said: “These figures are a truly shocking indictment of the SNP’s management of our NHS.
“It is utterly unacceptable that almost 1,000 people waited in A&E for over 12 hours last month, most likely in fear and pain.”
Scottish Labour health spokeswoman Monica Lennon accused the Scottish Government of complacency.