An Internal Audit vision statement must be carefully thought out and defined. It must be in line with the company's vision statement or else Audit will not be supporting the business. A vision statement needs to be simple comprehensive and direct.
An example of a vison statement for an audit department would be:
"To provide world class internal auditing services using all methods available to support the business in becoming a leader in it's industry."
The mission statement defines more of how the department is going to achieve this.