UI design - Include a Cancel button or not?

Question

We are designing the UI for a new line of business application. We have no real constraints and are free to design the UI as we see fit. The UI will be done in WPF and targeted for Windows 7, Vista, and XP Pro users.

Many dialog boxes contain OK and Cancel buttons in their lower right corner. Do you feel it is necessary to have this Cancel button or is the red X in the upper right corner sufficient? We are discussing this as we have been noticing more UIs that do not have cancel buttons, only the red X.

Answer 1

Not only you should add it but also make sure ESC is mapped to it.

Answer 2

Present the two designs to the customer - one with the "Cancel" button, the other without. See what their thoughts are.

Better still present them as partially working prototypes and watch them as they use the dialogs. If you ask them to perform a set of tasks and see if they have trouble when asked to cancel an operation.

Having said that, my preference is to include a "Cancel" button for the reasons others have mentioned:

• Accessibility (especially as Esc should be mapped to it).
• Convention (users will be expecting it).