BBC NEWS | Wales | Transplant list passes 500 mark
Donate Wales said in the last 20 weeks alone 13 people have died whilst on the waiting list.
Roy Thomas, the charity's chairman, said the figures of 501 on the waiting list underlined why it was "so important more of us who want to help should join the Organ Donor Register".
The charity launched its Tell a Loved One Campaign in May. Since then almost 14,000 have joined the register, but Mr Thomas said more are still needed with only 27% of the Welsh population signed up.
He said: "We would like to say thank you to those that have joined the Organ Donor Register in Wales and told their loved ones about their wishes, but the challenge does not stop there.
"We urge those that want to help to act on their good intentions and sign-up now. It only takes a few minutes to do so and you could save a life one day."