Causes and risk factors

We don’t know what causes CLL, but research is going on to find out more. There are a number of factors that can increase the risk of developing it.


The risk of developing CLL increases with age. Most people with CLL are over 60. It’s rare in people under 40.


CLL is more common in men than women.

Family history

Most people with CLL have no family history of it. But studies show that there is an increased risk of developing CLL if you have a first degree relative (parent, sibling or child) who has it. If anyone else in your family has CLL, it’s important to let your specialist know. However, most people who have a relative with CLL will never develop it themselves.


CLL is most common in people of European origin.

CLL is not infectious and cannot be passed on to other people.