The histopathological differentiation of bladder cancer is done by microscopy to describe the level of cell-differentiation. Well-differentiated means the cancer has more resemblance to normal bladder tissue and, therefore, tissue, and usually does not grow or spread quickly. Poorly differentiated tumors do not resemble the normal bladder usually grow quickly and spread to other regions earlier. The grade gives an idea of how fast the cancer might be growing or how aggressive it might be.
High grade cancers grow faster and spread earlier than low grade cancers.

There are three grades G1-G3, according to WHO grading, 1999:
· Well differentiated (G1)
· Moderately differentiated (G2)
· Poorly differentiated (G3)

The description GX might also be used, meaning the grade of differentiation can not be assessed.