Most cells in the body have a nucleus when they are mature. Here's a breakdown:

* Eukaryotic cells: The vast majority of cells in your body are eukaryotic. This means they have a nucleus that houses their genetic material (DNA).

* Exceptions: There are a few exceptions to this rule, namely red blood cells. Red blood cells lose their nucleus during development to make more room for hemoglobin, the protein responsible for carrying oxygen.

So, to answer your question more precisely, almost all mature cells in the body have a nucleus except for red blood cells.