The Irish Cancer Society has warned that there are nearly 1,000 people who have been waiting more than three months for a procedure for the diagnosis of bowel cancer.
New figures show there are now 951 people waiting more than three months for a colonoscopy on public hospital waiting lists, it said.
"While this represents a minor decrease of 4pc since the society published figures in March, it is the upward trend over the last six months that is most concerning. There are 130 more people waiting more than three months for a colonoscopy since December."
Kathleen O'Meara, of the Irish Cancer Society, said: "We are concerned at the potential impact the continued high number of people on waiting lists may have on a screening programme."
She said that they had welcomed Health Minister Mary Harney's announcement on bowel cancer screening which will involve the use of selected hospitals to deliver screening colonoscopies which will begin in 2012. "However, we believe that unless the problem of waiting lists is tackled in advance of screening being delivered, we are not sure that we can have full confidence in the ability of our hospital system to deliver screening while not impacting symptomatic services at the same time."
A year ago, Ms Harney told the HSE to ensure patients needing an urgent colonoscopy should not have to wait more than four weeks following referral from their GP.
It is now almost three years since mum-of-two Susie Long died from bowel cancer.
She came to national prominence after contacting Joe Duffy's Liveline show in January 2007, using the alias 'Rosie', and revealing that she had to wait seven months for a colonoscopy to diagnose her bowel cancer.
She died in October 2007.