RadListControl has two modes that determine how large an item will be. These modes are controlled by the AutoSizeItems property. Setting it to true will cause each item be as large as its content requires. Also in AutoSizeItems mode, the user can explicitly set the Height property of each RadListDataItem.
When AutoSizeItems is false on the other hand, the user can set the height of every item at once with the ItemHeight property of RadListControl. If users decide to set a large font for example, they either have to set AutoSizeItems to true so that the items can stretch to accommodate the large text or to remain with AutoSizeItems = false but set the ItemHeight property to some value that will be enough to display the whole text.