Latest statistics show Lothian has the second worst performance on overall waiting times in Scotland.
Just 73.1 per cent of patients went from referral to treatment within 18 weeks - well short of the Scottish Government target of 90 per cent.
Edinburgh Southern Labour MSP Daniel Johnson said the figures were “shocking” and called on the government to give Lothian support to meet the target.
Only four out of 15 health boards met the 90 per cent target. NHS Grampian was the only board worse than Lothian, with a figure of 70.1 per cent.
Across the country, 79.2 per cent of patients went from referral to treatment in 18 days.
Mr Johnson said: “It’s shocking that here in the capital we have the second worst waiting to treatment time in whole of Scotland.
“Over a quarter of people in the capital and in my constituency are waiting beyond 18 weeks going from referral to first treatment. The reality of that are people waiting months in pain for treatment that they were supposed to have been guaranteed by law by the SNP Scottish Government.
“This SNP Government has shown it is incapable of dealing with the problems affecting our NHS over and over again. What is our Health Secretary doing to make sure NHS Lothian receives the support it needs to meet targets?”
Joan Donnelly, acting chief officer for acute services at NHS Lothian, apologised to patients who had to wait longer than they should have.
She said: “We continue to work hard to reduce waiting times and are investing an additional £21.5m in this financial year to increase our immediate capacity.
“In the longer term we are also developing plans to create extra sustainable capacity such as the proposed development of a short-stay elective centre at St John’s Hospital, Livingston, to provide swifter access to procedures delivered on a day and short stay basis.”
The Scottish Government said it recognised patients were waiting too long for outpatient appointments as well as inpatient and day case procedures.
But it said it had invested more than £100m this year from its £850m Waiting Times Improvement plan.
A spokesman said: “We have been clear with health boards it is unacceptable for anyone to wait too long for treatment.”