Bowel cancer is the second most common cause of cancer death
Screening for bowel cancer in people aged 50 to 60 will not be introduced for seven years, the Welsh Assembly Government has admitted.
It has been committed to national screening scheme for everyone aged between 50 and 74 for several years.
But campaigners say they are deeply disappointed the programme's roll-out will not take place until 2015.
The assembly government said more time was needed to screen everyone in the age range from 50 to 74.
A spokesman said it had always intended to phase in the programme for men and women aged 50 to 74.
Screening for people aged 60 to 69 will begin this autumn, with screening for those aged 70 to 74 starting two years later.
But people aged between 50 and 60 will not be screened until 2015.
In England, the screening programme is already underway, but there are no plans to extend it beyond those aged 60 to 69.
Are they frightened by what they might find in the screening programme?
Nick Phillips, Bowel Cancer Wales
But in Scotland the screening of people aged between 50 and 74 is being phased in between 2007 and 2009.
Conservative health spokesman Jonathan Morgan said: "It is a national scandal that so many people in Wales die from an illness which can be treated if detected early enough.
"I fail to see why Wales cannot implement a national screening programme with the same speed as Scotland.
"The assembly government's failure to match this ambitious target could see people in Wales dying needlessly."
Nick Phillips, director of the campaigning group Bowel Cancer Wales, said he was very disappointed.
"The argument is that they do not have the capacity to do the work. Are they frightened by what they might find in the screening programme?" He said.
Mr Phillips's wife Marcia died of bowel cancer almost two years ago at the age of 45.
"Screening earlier would save lives," he added. "The sooner they bring it in the better."
Bowel cancer is the second biggest cancer killer in the UK after lung cancer but if caught early 90% of cases can be treated successfully.
Former AM Glyn Davies contracted bowel cancer almost six years ago at the age of 58, and made a good recovery after surgery.
I'm disappointed by the delays because we know that lives would be saved
"I know how lucky I was," said Mr Davies, now the president of the Campaign for the Protection of Rural Wales.
"The position of the tumour meant it could be discovered without screening but for most people that is not the case.
"I'm disappointed by the delays because we know that lives would be saved. We know that two in every 1,000 people who are screened have bowel cancer.
"There are hundreds of people walking round Wales with bowel cancer tumours and they don't know they've got them."
The spokesman for the Welsh Assembly Government said the bowel screening programme was on schedule to be introduced in October.
He added: "It is vital that the introduction of a screening programme does not disadvantage those that have symptoms suggestive of bowel disease.
"After detailed planning for the programme it became clear that more time would be needed for the roll-out."
He said that the phased implementation of screening programmes was in line with other programmes such as Breast Test Wales.