diff --git a/src/aces/__main__.py b/src/aces/__main__.py
index b0a4a9e..80f94ab 100644
--- a/src/aces/__main__.py
+++ b/src/aces/__main__.py
@@ -46,7 +46,7 @@ def main(cfg: DictConfig):
     result = query.query(task_cfg, predicates_df)
 
     if cfg.data.standard.lower() == "meds":
-        result = result.rename(columns={"subject_id": "patient_id"})
+        result = result.rename({"subject_id": "patient_id"})
 
     # save results to parquet
     os.makedirs(os.path.dirname(cfg.output_filepath), exist_ok=True)
diff --git a/src/aces/predicates.py b/src/aces/predicates.py
index c286650..bac82d2 100644
--- a/src/aces/predicates.py
+++ b/src/aces/predicates.py
@@ -207,6 +207,56 @@ def direct_load_plain_predicates(
     )
 
 
+def unnest_meds(data: pl.DataFrame) -> pl.DataFrame:
+    """Unnest MEDS data.
+
+    Single-nested MEDS has a row per patient, with all the observations aggregated into a list of "event"
+    structs. The events column needs to be exploded and unnested.
+
+    Args:
+        data: The Polars DataFrame containing the single-nested MEDS data.
+
+    Returns:
+        The Polars DataFrame with the events column exploded and unnested.
+
+    Example:
+        >>> data = pl.DataFrame({
+        ...     "subject_id": [1, 2, 3],
+        ...     "events": [
+        ...         [{"timestamp": None, "code": "EYE_COLOR//HAZEL", "numerical_value": None},
+        ...             {"timestamp": None, "code": "HEIGHT", "numerical_value": 160},
+        ...             {"timestamp": "3/9/1978 00:00", "code": "DOB", "numerical_value": None}],
+        ...         [{"timestamp": None, "code": "EYE_COLOR//BROWN", "numerical_value": None},
+        ...             {"timestamp": None, "code": "HEIGHT", "numerical_value": 175},
+        ...             {"timestamp": "12/28/1980 00:00", "code": "DOB", "numerical_value": None}],
+        ...         [{"timestamp": None, "code": "EYE_COLOR//BROWN", "numerical_value": None},
+        ...             {"timestamp": None, "code": "HEIGHT", "numerical_value": 166},
+        ...             {"timestamp": "12/19/1988 00:00", "code": "DOB", "numerical_value": None}],
+        ...     ],
+        ... })
+        >>> unnest_meds(data)
+        shape: (9, 4)
+        ┌────────────┬──────────────────┬──────────────────┬─────────────────┐
+        │ subject_id ┆ timestamp        ┆ code             ┆ numerical_value │
+        │ ---        ┆ ---              ┆ ---              ┆ ---             │
+        │ i64        ┆ str              ┆ str              ┆ i64             │
+        ╞════════════╪══════════════════╪══════════════════╪═════════════════╡
+        │ 1          ┆ null             ┆ EYE_COLOR//HAZEL ┆ null            │
+        │ 1          ┆ null             ┆ HEIGHT           ┆ 160             │
+        │ 1          ┆ 3/9/1978 00:00   ┆ DOB              ┆ null            │
+        │ 2          ┆ null             ┆ EYE_COLOR//BROWN ┆ null            │
+        │ 2          ┆ null             ┆ HEIGHT           ┆ 175             │
+        │ 2          ┆ 12/28/1980 00:00 ┆ DOB              ┆ null            │
+        │ 3          ┆ null             ┆ EYE_COLOR//BROWN ┆ null            │
+        │ 3          ┆ null             ┆ HEIGHT           ┆ 166             │
+        │ 3          ┆ 12/19/1988 00:00 ┆ DOB              ┆ null            │
+        └────────────┴──────────────────┴──────────────────┴─────────────────┘
+    """
+    logger.info("Found single-nested MEDS data, unnesting...")
+
+    return data.explode("events").unnest("events")
+
+
 def generate_plain_predicates_from_meds(data_path: Path, predicates: dict) -> pl.DataFrame:
     """Generate plain predicate columns from a MEDS dataset.
 
@@ -254,6 +304,9 @@ def generate_plain_predicates_from_meds(data_path: Path, predicates: dict) -> pl
         .drop_nulls(subset=["subject_id", "timestamp"])
     )
 
+    if data.columns == ["subject_id", "events"]:
+        data = unnest_meds(data)
+
     # generate plain predicate columns
     logger.info("Generating plain predicate columns...")
     for name, plain_predicate in predicates.items():