diff --git a/pytm/pytm.py b/pytm/pytm.py
index a193c6d..f50a367 100644
--- a/pytm/pytm.py
+++ b/pytm/pytm.py
@@ -98,8 +98,8 @@ def _setLabel(element):
     return "<br/>".join(wrap(element.name, 14))
 
 
-def _sort(elements, addOrder=False):
-    ordered = sorted(elements, key=lambda flow: flow.order)
+def _sort(flows, addOrder=False):
+    ordered = sorted(flows, key=lambda flow: flow.order)
     if not addOrder:
         return ordered
     for i, flow in enumerate(ordered):
@@ -109,6 +109,27 @@ def _sort(elements, addOrder=False):
     return ordered
 
 
+def _sort_elem(elements):
+    orders = {}
+    for e in elements:
+        try:
+            order = e.order
+        except AttributeError:
+            continue
+        if e.source not in orders or orders[e.source] > order:
+            orders[e.source] = order
+    m = max(orders.values()) + 1
+    return sorted(
+        elements,
+        key=lambda e: (
+            orders.get(e, m),
+            e.__class__.__name__,
+            getattr(e, "order", 0),
+            str(e),
+        ),
+    )
+
+
 def _match_responses(flows):
     """Ensure that responses are pointing to requests"""
     index = defaultdict(list)
@@ -138,8 +159,8 @@ def _match_responses(flows):
     return flows
 
 
-def _applyDefaults(elements):
-    for e in elements:
+def _apply_defaults(flows):
+    for e in flows:
         e._safeset("data", e.source.data)
         if e.isResponse:
             e._safeset("protocol", e.source.protocol)
@@ -152,6 +173,21 @@ def _applyDefaults(elements):
                 e._safeset("isEncrypted", e.sink.isEncrypted)
 
 
+def _get_elements_and_boundaries(flows):
+    """filter out elements and boundaries not used in this TM"""
+    elements = {}
+    boundaries = {}
+    for e in flows:
+        elements[e] = True
+        elements[e.source] = True
+        elements[e.sink] = True
+        if e.source.inBoundary is not None:
+            boundaries[e.source.inBoundary] = True
+        if e.sink.inBoundary is not None:
+            boundaries[e.sink.inBoundary] = True
+    return (elements.keys(), boundaries.keys())
+
+
 ''' End of help functions '''
 
 
@@ -215,6 +251,7 @@ class TM():
                             onSet=lambda i, v: i._init_threats())
     isOrdered = varBool(False)
     mergeResponses = varBool(False)
+    ignoreUnused = varBool(False)
 
     def __init__(self, name, **kwargs):
         for key, value in kwargs.items():
@@ -252,10 +289,15 @@ def resolve(self):
     def check(self):
         if self.description is None:
             raise ValueError("Every threat model should have at least a brief description of the system being modeled.")
-        _applyDefaults(TM._BagOfFlows)
+        _apply_defaults(TM._BagOfFlows)
+        if self.ignoreUnused:
+            TM._BagOfElements, TM._BagOfBoundaries = _get_elements_and_boundaries(TM._BagOfFlows)
         for e in (TM._BagOfElements):
             e.check()
         TM._BagOfFlows = _match_responses(_sort(TM._BagOfFlows, self.isOrdered))
+        if self.ignoreUnused:
+            # cannot rely on user defined order if assets are re-used in multiple models
+            TM._BagOfElements = _sort_elem(TM._BagOfElements)
 
     def dfd(self):
         print("digraph tm {\n\tgraph [\n\tfontname = Arial;\n\tfontsize = 14;\n\t]")
diff --git a/tests/seq_unused.plantuml b/tests/seq_unused.plantuml
new file mode 100644
index 0000000..a83cc7d
--- /dev/null
+++ b/tests/seq_unused.plantuml
@@ -0,0 +1,15 @@
+@startuml
+actor actor_User_579e9aae81 as "User"
+database datastore_SQLDatabase_d2006ce1bb as "SQL Database"
+entity server_WebServer_f2eb7a3ff7 as "Web Server"
+actor_User_579e9aae81 -> server_WebServer_f2eb7a3ff7: User enters comments (*)
+note left
+bbb
+end note
+server_WebServer_f2eb7a3ff7 -> datastore_SQLDatabase_d2006ce1bb: Insert query with comments
+note left
+ccc
+end note
+datastore_SQLDatabase_d2006ce1bb -> server_WebServer_f2eb7a3ff7: Retrieve comments
+server_WebServer_f2eb7a3ff7 -> actor_User_579e9aae81: Show comments (*)
+@enduml
diff --git a/tests/test_pytmfunc.py b/tests/test_pytmfunc.py
index c1f017b..3f1d968 100644
--- a/tests/test_pytmfunc.py
+++ b/tests/test_pytmfunc.py
@@ -49,6 +49,35 @@ def test_seq(self):
         Dataflow(db, web, "Retrieve comments")
         Dataflow(web, user, "Show comments (*)")
 
+        tm.check()
+        with captured_output() as (out, err):
+            tm.seq()
+
+        output = out.getvalue().strip()
+        self.maxDiff = None
+        self.assertEqual(output, expected)
+
+    def test_seq_unused(self):
+        random.seed(0)
+        dir_path = os.path.dirname(os.path.realpath(__file__))
+        with open(os.path.join(dir_path, 'seq_unused.plantuml')) as x:
+            expected = x.read().strip()
+
+        TM.reset()
+        tm = TM("my test tm", description="aaa", ignoreUnused=True)
+        internet = Boundary("Internet")
+        server_db = Boundary("Server/DB")
+        user = Actor("User", inBoundary=internet)
+        web = Server("Web Server")
+        db = Datastore("SQL Database", inBoundary=server_db)
+        Lambda("Unused Lambda")
+
+        Dataflow(user, web, "User enters comments (*)", note="bbb")
+        Dataflow(web, db, "Insert query with comments", note="ccc")
+        Dataflow(db, web, "Retrieve comments")
+        Dataflow(web, user, "Show comments (*)")
+
+        tm.check()
         with captured_output() as (out, err):
             tm.seq()
 
@@ -76,6 +105,7 @@ def test_dfd(self):
         Dataflow(db, web, "Retrieve comments")
         Dataflow(web, user, "Show comments (*)")
 
+        tm.check()
         with captured_output() as (out, err):
             tm.dfd()