A new HSE report has revealed waiting times of two years or more for colonoscopies, a check which should be performed within four weeks to look for cancer and other conditions.
It shows that there are 909 patients around the country waiting for a colonoscopy, a test that allows a doctor to see if there are any abnormal growths.
In December, Minister for Health Mary Harney told the HSE to comply with a target of access to a colonoscopy within four weeks of being referred by a doctor.
However, the HSE report reveals that 59 patients are waiting between one and two years and another five patients are waiting two years or more for a colonoscopy.
On average, over 29% of patients are waiting in excess of three months for the cancer check.
According to the HSE, Tallaght Hospital in Dublin has the largest number of patients on a colonoscopy waiting list - with 49 patients waiting for up to two years and four patients waiting longer than that period for the check.
At the Mercy Hospital in Cork, one patient is waiting over two years for a colonoscopy.
The HSE says Tallaght Hospital is working with the National Treatment Purchase Fund, which secures private treatment, to speed up the timely referral of patients.
According to the report, a small number of patients at the following hospitals are also waiting up to two years for a colonoscopy: in Dublin, St Vincent's, Dublin (one patient), Beaumont Hospital, (one patient) and at Our Lady's Hospital for Children in Crumlin (three patients).
Outside of Dublin the figures are: the Midland Regional Tullamore (three patients) and the Midland Regional Limerick (two patients).
Hospitals with patients waiting over three months are being asked to refer these to the NTPF and a validation of colonoscopy waiting lists over a year is also under way.
The Irish Cancer Society has described the figures as unacceptable.
In a statement, the HSE said it has an agreement with the NTPF, whereby any public patient in need of an urgent colonoscopy can be seen as a priority and treated privately.
It also said that the overall number of patients waiting longer than three months had reduced significantly since last October.