diff --git a/release_notes.md b/release_notes.md
index 8150a3a9..9a112989 100644
--- a/release_notes.md
+++ b/release_notes.md
@@ -585,6 +585,7 @@ If you want to use RDP you have to specify dependency in square brackets `[ ]`
 8. [TH2-5201] Performance improvements have been made to converters:
 9. [TH2-5101] Data.update_metadata() now takes `change_type` argument (values: `update` default, `change` which denotes 
 whether to update or overwrite with new values.
+10. [TH2-5099] Fixed slow iteration for Data objects created with many addition operators.
 
 Benchmark.
 - 1mln iterations per test
diff --git a/tests/tests_unit/test_data/test_performance/iteration_on_data_files.py b/tests/tests_unit/test_data/test_performance/iteration_on_data_files.py
new file mode 100644
index 00000000..f0d1b3f5
--- /dev/null
+++ b/tests/tests_unit/test_data/test_performance/iteration_on_data_files.py
@@ -0,0 +1,57 @@
+import os
+import time
+import random
+
+from th2_data_services.data import Data
+
+
+def get_iteration_speed_plus():
+    data = Data.from_json(f"benchmark/json0.gz", gzip=True)
+    for i in range(1, 122):
+        data = data + Data.from_json(f"benchmark/json{i}.gz", gzip=True)
+
+    _iterate_and_print_stats(data)
+
+
+def get_iteration_speed_plus_equals():
+    data = Data.from_json(f"benchmark/json0.gz", gzip=True)
+    for i in range(1, 122):
+        data += Data.from_json(f"benchmark/json{i}.gz", gzip=True)
+
+    _iterate_and_print_stats(data)
+
+
+def get_iteration_speed_list_comprehension():
+    data = Data([Data.from_json(f"benchmark/json{i}.gz", gzip=True) for i in range(122)])
+
+    _iterate_and_print_stats(data)
+
+
+def _generate_data():
+    n = 10_000
+    data = Data([random.randint(1, 100_000) for _ in range(n)])
+    os.makedirs("benchmark", exist_ok=True)
+    data.to_json_lines(f"benchmark/json0.gz", gzip=True, overwrite=True)
+    for i in range(1, 122):
+        data = Data([random.randint(1, 100_000) for _ in range(n)])
+        data.to_json_lines(f"benchmark/json{i}.gz", gzip=True, overwrite=True)
+
+
+def _iterate_and_print_stats(data):
+    start_time = time.time()
+    j = 0
+    for _ in data:
+        j += 1
+
+    print(f"Number of records iterated: {j}")
+    print(f"Time took: {time.time() - start_time} seconds")
+
+
+if __name__ == "__main__":
+    _generate_data()
+    print("get_iteration_speed_plus()")
+    get_iteration_speed_plus()
+    print("get_iteration_speed_plus_equals()")
+    get_iteration_speed_plus_equals()
+    print("get_iteration_speed_list_comprehension()")
+    get_iteration_speed_list_comprehension()
diff --git a/th2_data_services/data.py b/th2_data_services/data.py
index ae779abf..76311f73 100644
--- a/th2_data_services/data.py
+++ b/th2_data_services/data.py
@@ -201,6 +201,7 @@ def __init__(
         self._pending_cache_path = (
             self._cache_path.with_name("[PENDING]" + self._cache_filename).resolve().absolute()
         )
+        self._data_list = [self]
         self._cache_file_obj: Optional[BinaryIO] = None
         self._len: Optional[int] = None
         self.workflow = DataWorkflow()
@@ -255,7 +256,9 @@ def __add__(self, other_data: "Data") -> "Data[DataIterValues]":
         """
         if not isinstance(other_data, Data):
             raise TypeError("Addition only works between Data objects")
-        data = Data(self._create_data_set_from_iterables([self, other_data]))
+        new_data_list = self._data_list + other_data._data_list
+        data = Data(new_data_list)
+        data._data_list = new_data_list
         data._set_metadata(self.metadata)
         if "source_file" in data.metadata:
             data.update_metadata({"source_files": [data.metadata["source_file"]]})