relationship

[boycalledsue]

what relation to me is my mother's cousins son?

[chazza]

second cousin

[Leigh21Leigh]

i believe that is your second cousin, once removed.

[Solarjunkie]

First cousin, once removed.
His relationship to your son would be second cousin.

[chazza]

As you have had a few different answers, I will explain my answer a bit more clearly with the help of wikipedia's diagram

http://upload.wikimedia.org/wikipedia/en/thumb /5/5d/Cousin_tree.png/500px-Cousin_tree.png

Obviously you are the "you" on the diagram, your mum is the "mother" above you, her cousin is the "first cousin once removed" (ie once removed from you, the green box), and the cousins child is the one below that ie second cousin.

The removed bit refers to how many generations difference there are between you and the person concerned. As this is your mothers cousins child, you are the same generation as that child and therefore not removed at all!

[thussain]

definitely second cousin
you use once removed when 1 generation different, i.e. your mum's cousin is your cousin once removed. As your the same generation as your mum's cousin son then there is no "removed"

[Dark Angel]

Your mother's cousin's son is your second cousin.

Your first cousin's offspring are your first cousin once removed.