An insurance office has 65 employees. If 52 of the employees have cellular phones, what portion of the employees do not have cellular phones?

The number of employees without cellular phones is 65 employees - 52 employees = <<65-52=13>>13 employees.

Thus, 13 employees/65 employees = <<13/65=0.2>>0.2 = <<0.2*100=20>>20%. Answer: \boxed{20}.