More than a quarter of patients at NHS Grampian were forced to wait more than 18 weeks for treatment.
Shock new figures have revealed the north-east health board has the second worst waiting times in the country.
A fifth of patients at NHS Highland were also delayed for more than the Scottish Government of 18 weeks, according to official figures.
The waiting times – which are at their worst level across the country in five years – have provoked a furious backlash from opposition politicians, who have branded them “simply not good enough”.
Health Secretary Shona Robison admitted the performance was “short” of expectations, but said the government was investing £10million to cut waiting lists.
But Aberdeenshire West MSP Alexander Burnett said: “This is just the latest symptom of the SNP’s ongoing failure to properly manage our health service in Grampian.
“There is a crisis in GP recruitment, millions of pounds are spent plugging gaps with agency staff, patients are sent out of the area for treatment and now the length of time from referral to operations is revealed to be the second worst in Scotland.
“And despite these mounting problems under the watch of the SNP, we hear that the Scottish Government is underfunding NHS Grampian to the tune of £12million.
“It is simply not good enough, and people in the north-east deserve better.”
Figures for September show that NHS Grampian treated 74.6% of patients within the 18-week target, rising to 79.8% in NHS Highland.
Scottish Labour’s health spokesman Anas Sarwar added: “These damning figures show the consequences of the SNP’s mismanagement of the NHS.
“Declining performance in key areas means patients are waiting longer for treatment. That just isn’t good enough.”
A spokeswoman for NHS Grampian said the waiting times were partly caused by staff shortages.
She added: “Where we do not achieve the waiting standards set we actively manage the lists and ensure that patients are treated as soon as possible and in line with their clinical priority.”
A spokesman for NHS Highland added: “Clearly there are challenges delivering the 18 week referral to treatment and some patients are waiting longer than we would wish.
“We have plans in place to improve performance in this area.”
Health Secretary Ms Robison said: “The performance of our hospitals in scheduled care is simply short of what we expect and that is why we’ve put in an extra £10million this month to deliver an extra 40,000 outpatient appointments.
“There are also a number of local areas and local clinical teams that are doing some excellent work at the moment to redesign the way they provide outpatient services.
“It is important that this work is shared across the health service and we will be taking that forward, as well as working with boards with particular challenges to get their services back on a sustainable footing.”