diff --git a/atlas/filters.py b/atlas/filters.py
index 1da6b22f..a86ed2b8 100755
--- a/atlas/filters.py
+++ b/atlas/filters.py
@@ -164,13 +164,16 @@ class SeriesFilter(django_filters.FilterSet):
 
 
 class ConditionFilter(django_filters.FilterSet):
+    # Replace legacy `primary` filter with `is_canonical` and provide a
+    # `synonym` filter which will filter by the canonical group of the
+    # selected condition.
+    is_canonical = django_filters.BooleanFilter(method="filter_is_canonical", label="Canonical")
+    synonym = django_filters.ModelChoiceFilter(queryset=Condition.objects.all(), method="filter_synonym", label="Synonym group")
+
     class Meta:
         model = Condition
         fields = {
             "name": ["icontains"],
-            "primary": ["exact"],
-            "synonym": ["exact"],
-            #"parent": ["exact"],
             "subspecialty": ["exact"],
             "rcr_curriculum": ["exact"],
         }
@@ -189,6 +192,21 @@ class ConditionFilter(django_filters.FilterSet):
         )
         pass
 
+    def filter_is_canonical(self, queryset, name, value):
+        if value in (True, "True", "true", 1, "1"):
+            return queryset.filter(canonical__isnull=True)
+        if value in (False, "False", "false", 0, "0"):
+            return queryset.filter(canonical__isnull=False)
+        return queryset
+
+    def filter_synonym(self, queryset, name, value):
+        # value is a Condition instance selected in the filter. Return all
+        # Conditions that belong to the same canonical group as `value`.
+        if not value:
+            return queryset
+        master = value.canonical if value.canonical else value
+        return queryset.filter(Q(canonical=master) | Q(pk=master.pk))
+
 
 class FindingFilter(django_filters.FilterSet):
     class Meta: