diff -r a7c05bde7b65 src/widgets/dropdown.cpp
--- a/src/widgets/dropdown.cpp	Thu Feb 25 21:13:50 2010 +0000
+++ b/src/widgets/dropdown.cpp	Thu Feb 25 22:35:46 2010 +0100
@@ -402,6 +402,23 @@
 	new DropdownWindow(w, list, selected, button, instant_close, dw_pos, dw_size, wi_colour, scroll);
 }
 
+/* Builds a DropDownList from a StringID array. */
+bool BuildDropDownList(DropDownList *list, const StringID *strings, uint32 disabled_mask, uint32 hidden_mask) {
+	for (uint i = 0; strings[i] != INVALID_STRING_ID; i++) {
+		if (!HasBit(hidden_mask, i)) {
+			list->push_back(new DropDownListStringItem(strings[i], i, HasBit(disabled_mask, i)));
+		}
+	}
+
+	/* No entries in the list? */
+	if (list->size() == 0) {
+		DeleteDropDownList(list);
+		return false;
+	}
+
+	return true;
+}
+
 /** Show a dropdown menu window near a widget of the parent window.
  * The result code of the items is their index in the #strings list.
  * @param w             Parent window that wants the dropdown menu.
@@ -416,19 +433,8 @@
 {
 	DropDownList *list = new DropDownList();
 
-	for (uint i = 0; strings[i] != INVALID_STRING_ID; i++) {
-		if (!HasBit(hidden_mask, i)) {
-			list->push_back(new DropDownListStringItem(strings[i], i, HasBit(disabled_mask, i)));
-		}
-	}
-
-	/* No entries in the list? */
-	if (list->size() == 0) {
-		DeleteDropDownList(list);
-		return;
-	}
-
-	ShowDropDownList(w, list, selected, button, width);
+	if (BuildDropDownList(list, strings, disabled_mask, hidden_mask))
+		ShowDropDownList(w, list, selected, button, width);
 }
 
 /**
@@ -454,3 +460,70 @@
 	return -1;
 }
 
+void DoScrollDropDownList(Window *w, const DropDownList *list, const int selected, int button, int wheel)
+{
+	assert(list != NULL);
+	assert(w != NULL);
+	/* Ensure that we are scrolling */
+	if (wheel == 0) return;
+
+	/* Search the currently selected item */
+	DropDownList::const_iterator it = list->begin();
+	for (; it != list->end(); ++it) {
+		if (((DropDownListItem *) *it)->result == selected) break;
+	}
+	/* The currently selected item wasn't found */
+	if (it == list->end()) return;
+
+	/* Only scrolls from one item at the time */
+	wheel = wheel > 0 ? 1 : -1;
+
+	const DropDownListItem *bound = wheel > 0 ? list->back() : list->front();
+	/* Don't scrolls if we already are at list bounds */
+	if (((DropDownListItem *) *it) == bound) return;
+
+	int new_index = selected;
+	do {
+		/* Select the next item (it += wheel) */
+		wheel > 0 ? it++ : it--;
+		const DropDownListItem * item = *it;
+		if (!item->masked && item->Selectable()) {
+			/* The next item is valid */
+			new_index = item->result;
+			break;
+		}
+	} while (((DropDownListItem *) *it) != bound);
+
+	/* Returns false if the selected item hasn't change */
+	if (new_index == selected) return;
+
+	/* If the dropdown window was opened, close it */
+	DeleteWindowById(WC_DROPDOWN_MENU, 0);
+	/* Simulate a click on the item in the dropdown window */
+	w->OnDropdownSelect(button, new_index);
+}
+
+void ScrollDropDownList(Window *w, DropDownList *list, int selected, int button, int wheel)
+{
+	DoScrollDropDownList(w, list, selected, button, wheel);
+	DeleteDropDownList(list);
+}
+
+/**
+ * Scrolls a drop down menu.
+ * The result code of the items is their index in the #strings list.
+ * @param w             Parent window that wants the dropdown menu.
+ * @param strings       Menu list, end with #INVALID_STRING_ID
+ * @param selected      Index of initial selected item.
+ * @param button        Button widget number of the parent window #w that wants the dropdown menu.
+ * @param disabled_mask Bitmask for diabled items (items with their bit set are not copied to the dropdown list).
+ * @param hidden_mask   Bitmask for hidden items (items with their bit set are displayed, but not selectable in the dropdown list).
+ * @param wheel         The mouse wheel direction in which we should scroll the list
+ */
+void ScrollDropDownMenu(Window *w, const StringID *strings, int selected, int button, uint32 disabled_mask, uint32 hidden_mask, int wheel)
+{
+	DropDownList *list = new DropDownList();
+
+	if (BuildDropDownList(list, strings, disabled_mask, hidden_mask))
+		ScrollDropDownList(w, list, selected, button, wheel);
+}
diff -r a7c05bde7b65 src/widgets/dropdown_func.h
--- a/src/widgets/dropdown_func.h	Thu Feb 25 21:13:50 2010 +0000
+++ b/src/widgets/dropdown_func.h	Thu Feb 25 22:35:46 2010 +0100
@@ -20,4 +20,6 @@
 /* Hide drop down menu of a parent window */
 int HideDropDownMenu(Window *pw);
 
+/* Scroll drop down menu containing a fixed list of strings */
+void ScrollDropDownMenu(Window *w, const StringID *strings, int selected, int button, uint32 disabled_mask, uint32 hidden_mask, int wheel);
 #endif /* WIDGETS_DROPDOWN_FUNC_H */
diff -r a7c05bde7b65 src/widgets/dropdown_type.h
--- a/src/widgets/dropdown_type.h	Thu Feb 25 21:13:50 2010 +0000
+++ b/src/widgets/dropdown_type.h	Thu Feb 25 22:35:46 2010 +0100
@@ -99,4 +99,14 @@
  */
 void ShowDropDownList(Window *w, DropDownList *list, int selected, int button, uint width = 0, bool auto_width = false, bool instant_close = false);
 
+/**
+ * Scrolls a drop down list.
+ * @param w        Parent window for the list.
+ * @param list     Prepopulated DropDownList. Will be deleted when the list is
+ *                 closed.
+ * @param selected The initially selected list item.
+ * @param button   The widget within the parent window that should be scrolled.
+ * @param wheel    The mouse wheel direction in which we should scroll the list
+ */
+void ScrollDropDownList(Window *w, DropDownList *list, int selected, int button, int wheel);
 #endif /* WIDGETS_DROPDOWN_TYPE_H */