diff --git a/src/comp/driver/rustc.rs b/src/comp/driver/rustc.rs
index d83e04e061a..55dcc35a637 100644
--- a/src/comp/driver/rustc.rs
+++ b/src/comp/driver/rustc.rs
@@ -80,6 +80,8 @@ fn compile_input(session::session sess, eval::env env, str input,
     auto crate =
         time(time_passes, "parsing", bind parse_input(sess, p, input));
     if (sess.get_opts().output_type == link::output_type_none) { ret; }
+    crate = time(time_passes, "configuration",
+                 bind front::config::strip_unconfigured_items(crate));
     auto ast_map = time(time_passes, "ast indexing",
                         bind middle::ast_map::map_crate(*crate));
     auto d =
diff --git a/src/comp/front/config.rs b/src/comp/front/config.rs
new file mode 100644
index 00000000000..04429481b5a
--- /dev/null
+++ b/src/comp/front/config.rs
@@ -0,0 +1,68 @@
+import std::option;
+import std::vec;
+import ast;
+import fold;
+import attr;
+
+export strip_unconfigured_items;
+
+// Support conditional compilation by transforming the AST, stripping out
+// any items that do not belong in the current configuration
+fn strip_unconfigured_items(@ast::crate crate) -> @ast::crate {
+    auto cfg = crate.node.config;
+
+    auto precursor = rec(fold_mod = bind fold_mod(cfg, _, _)
+                         with *fold::default_ast_fold());
+
+    auto fold = fold::make_fold(precursor);
+    auto res = @fold.fold_crate(*crate);
+    // FIXME: This is necessary to break a circular reference
+    fold::dummy_out(fold);
+    ret res;
+}
+
+fn filter_item(&ast::crate_cfg cfg,
+               &@ast::item item) -> option::t[@ast::item] {
+    if (in_cfg(cfg, item)) {
+        option::some(item)
+    } else {
+        option::none
+    }
+}
+
+fn fold_mod(&ast::crate_cfg cfg, &ast::_mod m,
+              fold::ast_fold fld) -> ast::_mod {
+    auto filter = bind filter_item(cfg, _);
+    auto filtered_items = vec::filter_map(filter, m.items);
+    ret rec(view_items=vec::map(fld.fold_view_item, m.view_items),
+            items=vec::map(fld.fold_item, filtered_items));
+}
+
+// Determine if an item should be translated in the current crate
+// configuration based on the item's attributes
+fn in_cfg(&ast::crate_cfg cfg, &@ast::item item) -> bool {
+
+    auto item_cfg_attrs = attr::find_attrs_by_name(item.attrs, "cfg");
+
+    auto item_has_cfg_attrs = vec::len(item_cfg_attrs) > 0u;
+    if (!item_has_cfg_attrs) { ret true; }
+
+    auto item_cfg_metas = attr::attr_metas(item_cfg_attrs);
+
+    for (@ast::meta_item cfg_mi in item_cfg_metas) {
+        if (attr::contains(cfg, cfg_mi)) {
+            ret true;
+        }
+    }
+
+    ret false;
+}
+
+
+// Local Variables:
+// fill-column: 78;
+// indent-tabs-mode: nil
+// c-basic-offset: 4
+// buffer-file-coding-system: utf-8-unix
+// compile-command: "make -k -C $RBUILD 2>&1 | sed -e 's/\\/x\\//x:\\//g'";
+// End:
diff --git a/src/comp/rustc.rc b/src/comp/rustc.rc
index 6b87ce624fa..0fb9f233255 100644
--- a/src/comp/rustc.rc
+++ b/src/comp/rustc.rc
@@ -57,6 +57,7 @@ mod front {
     mod parser;
     mod token;
     mod eval;
+    mod config;
 }
 
 mod back {