The DropDownList control does not expose a sort method to sort items by either the value or the displayed text.

If you pull the values from database, it's very simple because you just add the ORDER BY clause in the SQL SELECT statement.
But if you can't access on the database to modify the stored procedure or view, the solution is to load your data into an array and associate this to the combobox or dropdownlist.

With these simple lines, you can do it.

        private void btnSort_Click(object sender, EventArgs e)
        {
            ArrayList cboItems = new ArrayList();

            foreach (string item in cboCities.Items)
            {
                cboItems.Add(item);
                cboItems.TrimToSize();
            }

            cboItems.Sort();
            cboCities.Items.Clear();
            string[] Items = new string[cboItems.Count];

            cboItems.CopyTo(Items);
            cboCities.Items.AddRange(Items);
        }

 With some little fix, you can switch from combobox to dropdownlist.
On the link below you can find the source code with an example.

SortedList.zip (32.22 kb)