Conservative MS Paul Davies has been diagnosed with prostate cancer.
The Senedd Member for Preseli Pembrokeshire said on Twitter that he is soon due to begin treatment which will be ongoing over the coming months.
The former Welsh Conservative leader praised NHS staff for their support and advice.
He said in a statement: "This week I met my consultant to discuss treatment options, following a recent diagnosis of prostate cancer. I'll soon be starting treatment, which will be ongoing over the coming months.
"The service I've received so far has been second to none and I'm very grateful to the NHS staff that are looking after me for their advice and support."
Mr Davies used the opportunity to urge others to get checked out.
He said: "As I begin that treatment process, I want to remind everyone that it's so important to listen to your body and contact your GP if you feel that something isn't quite right.
"There is a wealth of information and guidance out there about prostate cancer and so please take a moment to remind yourself of the symptoms and the risk factors."
Mr Davies added: "In the meantime, my office remains open and I will continue to carry out my duties to the best of my ability."
It comes just days after Cardiff MP Kevin Brennan said he had recently undergone surgery for prostate cancer.
The Labour MP said he was "recuperating very well and should require no further treatment" and thanked NHS staff for their "incredible skill, professionalism, dedication and humanity".