diff --git a/src/biotite/structure/__init__.py b/src/biotite/structure/__init__.py
index df9776324..c8ecec129 100644
--- a/src/biotite/structure/__init__.py
+++ b/src/biotite/structure/__init__.py
@@ -57,14 +57,15 @@
 The following annotation categories are optionally used by some
 functions:
 
-=========  ===========  =================   ============================
+=========  ===========  =================   =========================================
 Category   Type         Examples            Description
-=========  ===========  =================   ============================
+=========  ===========  =================   =========================================
 atom_id    int          1,2,3, ...          Atom serial number
 b_factor   float        0.9, 12.3, ...      Temperature factor
 occupancy  float        .1, .3, .9, ...     Occupancy
 charge     int          -2,-1,0,1,2, ...    Electric charge of the atom
-=========  ===========  =================   ============================
+sym_id     string       '1','2','3', ...    Symmetry ID for assemblies/symmetry mates
+=========  ===========  =================   =========================================
 
 For each type, the attributes can be accessed directly.
 Both :class:`AtomArray` and :class:`AtomArrayStack` support
diff --git a/src/biotite/structure/io/pdb/convert.py b/src/biotite/structure/io/pdb/convert.py
index 127e49fbb..1971bc1ef 100644
--- a/src/biotite/structure/io/pdb/convert.py
+++ b/src/biotite/structure/io/pdb/convert.py
@@ -218,6 +218,8 @@ def get_assembly(
     assembly : AtomArray or AtomArrayStack
         The assembly.
         The return type depends on the `model` parameter.
+        Contains the `sym_id` annotation, which enumerates the copies of the asymmetric
+        unit in the assembly.
 
     Examples
     --------
diff --git a/src/biotite/structure/io/pdb/file.py b/src/biotite/structure/io/pdb/file.py
index 6d192dac6..2235cb1fa 100644
--- a/src/biotite/structure/io/pdb/file.py
+++ b/src/biotite/structure/io/pdb/file.py
@@ -790,6 +790,8 @@ def get_assembly(
         assembly : AtomArray or AtomArrayStack
             The assembly.
             The return type depends on the `model` parameter.
+            Contains the `sym_id` annotation, which enumerates the copies of the
+            asymmetric unit in the assembly.
 
         Examples
         --------
diff --git a/src/biotite/structure/io/pdbx/convert.py b/src/biotite/structure/io/pdbx/convert.py
index 8d3c52f41..dfb18ad96 100644
--- a/src/biotite/structure/io/pdbx/convert.py
+++ b/src/biotite/structure/io/pdbx/convert.py
@@ -1557,7 +1557,10 @@ def get_assembly(
     Returns
     -------
     assembly : AtomArray or AtomArrayStack
-        The assembly. The return type depends on the `model` parameter.
+        The assembly.
+        The return type depends on the `model` parameter.
+        Contains the `sym_id` annotation, which enumerates the copies of the asymmetric
+        unit in the assembly.
 
     Examples
     --------