diff --git a/README.md b/README.md
index e030c40..51efedb 100644
--- a/README.md
+++ b/README.md
@@ -164,14 +164,14 @@ result = md.convert("test.pdf")
 print(result.text_content)
 ```
 
-To use Large Language Models for image descriptions, provide `llm_client` and `llm_model`:
+To use Large Language Models for image descriptions (currently only for pptx and image files), provide `llm_client` and `llm_model`:
 
 ```python
 from markitdown import MarkItDown
 from openai import OpenAI
 
 client = OpenAI()
-md = MarkItDown(llm_client=client, llm_model="gpt-4o")
+md = MarkItDown(llm_client=client, llm_model="gpt-4o", llm_prompt="optional custom prompt")
 result = md.convert("example.jpg")
 print(result.text_content)
 ```
diff --git a/packages/markitdown/src/markitdown/_markitdown.py b/packages/markitdown/src/markitdown/_markitdown.py
index 3027efc..702b10c 100644
--- a/packages/markitdown/src/markitdown/_markitdown.py
+++ b/packages/markitdown/src/markitdown/_markitdown.py
@@ -115,6 +115,7 @@ class MarkItDown:
         # TODO - remove these (see enable_builtins)
         self._llm_client: Any = None
         self._llm_model: Union[str | None] = None
+        self._llm_prompt: Union[str | None] = None
         self._exiftool_path: Union[str | None] = None
         self._style_map: Union[str | None] = None
 
@@ -139,6 +140,7 @@ class MarkItDown:
             # TODO: Move these into converter constructors
             self._llm_client = kwargs.get("llm_client")
             self._llm_model = kwargs.get("llm_model")
+            self._llm_prompt = kwargs.get("llm_prompt")
             self._exiftool_path = kwargs.get("exiftool_path")
             self._style_map = kwargs.get("style_map")
 
@@ -559,6 +561,9 @@ class MarkItDown:
                 if "llm_model" not in _kwargs and self._llm_model is not None:
                     _kwargs["llm_model"] = self._llm_model
 
+                if "llm_prompt" not in _kwargs and self._llm_prompt is not None:
+                    _kwargs["llm_prompt"] = self._llm_prompt
+
                 if "style_map" not in _kwargs and self._style_map is not None:
                     _kwargs["style_map"] = self._style_map
 
diff --git a/packages/markitdown/tests/test_module_misc.py b/packages/markitdown/tests/test_module_misc.py
index 447e28a..03e123d 100644
--- a/packages/markitdown/tests/test_module_misc.py
+++ b/packages/markitdown/tests/test_module_misc.py
@@ -4,6 +4,7 @@ import os
 import re
 import shutil
 import pytest
+from unittest.mock import MagicMock
 
 from markitdown._uri_utils import parse_data_uri, file_uri_to_path
 
@@ -370,6 +371,50 @@ def test_markitdown_exiftool() -> None:
         assert target in result.text_content
 
 
+def test_markitdown_llm_parameters() -> None:
+    """Test that LLM parameters are correctly passed to the client."""
+    mock_client = MagicMock()
+    mock_response = MagicMock()
+    mock_response.choices = [
+        MagicMock(
+            message=MagicMock(
+                content="Test caption with red circle and blue square 5bda1dd6"
+            )
+        )
+    ]
+    mock_client.chat.completions.create.return_value = mock_response
+
+    test_prompt = "You are a professional test prompt."
+    markitdown = MarkItDown(
+        llm_client=mock_client, llm_model="gpt-4o", llm_prompt=test_prompt
+    )
+
+    # Test image file
+    markitdown.convert(os.path.join(TEST_FILES_DIR, "test_llm.jpg"))
+
+    # Verify the prompt was passed to the OpenAI API
+    assert mock_client.chat.completions.create.called
+    call_args = mock_client.chat.completions.create.call_args
+    messages = call_args[1]["messages"]
+    assert len(messages) == 1
+    assert messages[0]["content"][0]["text"] == test_prompt
+
+    # Reset the mock for the next test
+    mock_client.chat.completions.create.reset_mock()
+
+    # TODO: may only use one test after the llm caption method duplicate has been removed:
+    # https://github.com/microsoft/markitdown/pull/1254
+    # Test PPTX file
+    markitdown.convert(os.path.join(TEST_FILES_DIR, "test.pptx"))
+
+    # Verify the prompt was passed to the OpenAI API for PPTX images too
+    assert mock_client.chat.completions.create.called
+    call_args = mock_client.chat.completions.create.call_args
+    messages = call_args[1]["messages"]
+    assert len(messages) == 1
+    assert messages[0]["content"][0]["text"] == test_prompt
+
+
 @pytest.mark.skipif(
     skip_llm,
     reason="do not run llm tests without a key",
@@ -408,6 +453,7 @@ if __name__ == "__main__":
         test_speech_transcription,
         test_exceptions,
         test_markitdown_exiftool,
+        test_markitdown_llm_parameters,
         test_markitdown_llm,
     ]:
         print(f"Running {test.__name__}...", end="")