1private void AdjustComboBoxDropDownListWidth(object comboBox)
2{
3    Graphics g = null;
4    Font font = null;
5    try
6    {
7        ComboBox senderComboBox = null;
8        if (comboBox is ComboBox)
9            senderComboBox = (ComboBox)comboBox;
10        else if (comboBox is ToolStripComboBox)
11            senderComboBox = ((ToolStripComboBox)comboBox).ComboBox;
12        else
13            return;
14
15        int width = senderComboBox.Width;
16        g = senderComboBox.CreateGraphics();
17        font = senderComboBox.Font;
18
19        //checks if a scrollbar will be displayed.
20        //If yes, then get its width to adjust the size of the drop down list.
21        int vertScrollBarWidth =
22            (senderComboBox.Items.Count > senderComboBox.MaxDropDownItems)
23            ? SystemInformation.VerticalScrollBarWidth : 0;
24
25        int newWidth;
26        foreach (object s in senderComboBox.Items)  //Loop through list items and check size of each items.
27        {
28            if (s != null)
29            {
30                newWidth = (int)g.MeasureString(s.ToString().Trim(), font).Width
31                    + vertScrollBarWidth;
32                if (width < newWidth)
33                    width = newWidth;   //set the width of the drop down list to the width of the largest item.
34            }
35        }
36        senderComboBox.DropDownWidth = width;
37    }
38    catch
39    { }
40    finally
41    {
42        if (g != null)
43            g.Dispose();
44    }
45}