Figures show the majority of health boards are missing the goal to start treating 95 per cent of cancer patients urgently referred to hospital within two months.
Across the country 91.5 per cent of patients are treated in time - this is a sudden drop from about 94.5 per cent over the last year and compares to almost 97 per cent in 2011.
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Borders, Dumfries and Galloway, Ayrshire and Arran, Lanarkshire and Orkney are the only Scottish boards meeting the goal.
In Grampian 85.6 per cent of patients are treated in time and in Greater Glasgow and Clyde the figure is 90.9 per cent.
Support teams have already been sent into struggling health boards and Scottish Health Secretary Alex Neil has announced another £2.5 million to bring about improvements.
Jim Hume, health spokesman for the Scottish Liberal Democrats, said the NHS seemed to be going backwards on Mr Neil's watch. He added: "These figures will not come as a surprise to patients who have had to wait beyond the 62-day standard waiting time from referral to first cancer treatment - 62 days alone will feel like decades to cancer patients and their families as they wait to receive their first treatment."
Waiting times have improved significantly since the SNP came to power in 2007. Health boards recorded an average performance of 84.5 per cent that year. Under the watch of former SNP Health Secretary Nicola Sturgeon the NHS hit the 95 per cent aim for the first time. Since 2010, thousands more patients diagnosed through screening programmes have been included in the goal to ensure treatment - such as surgery or radiotherapy - starts within 62 days of an urgent referral to hospital with suspected cancer.
However, in recent financial quarters health boards have begun to slip slightly behind. The latest figures, released yesterday by the Information Services Division of the Scottish NHS along with 10 other sets of data, showed a sudden drop.
Jackson Carlaw, for the Scottish Conservatives, said: "What on earth have ministers been doing over the past year to allow this disgraceful situation to take hold?
"These are not patients sent on a whim for a check-up - we are talking about those deemed to need 'urgent' surgery on account of them probably having cancer."
Neil Findlay, for Scottish Labour, said it was "bitterly disappointing" that the target had again been missed.
Mr Neil said the figures, which cover January to March, reflected a period of time before the support teams got to work. Measures such as additional frontline staff, new theatres and an investment in diagnostic equipment are expected to now be making a difference.
He also pointed out the average length of time a patient waits to start their cancer treatment in Scotland is six days.
He added the NHS was consistently meeting the target to commence treating newly- diagnosed cancers within 31 days of agreeing the therapy or operation required.