Unique values in list

[C# Programming]

I am using MVC3 with razor and binding dropdownlist with a list

Now issue is

@Html.DropDownListFor(model => model.Result, new SelectList(Model.Result.OrderBy(item => item.Enhet), "EnhetID", "Enhet"), "ALL")
in Enhet i am getting 3 values

Nitin
NA
NA

I want to make sure that values are always unique, how can i remove duplicate values.