diff --git a/contrib/trials-cleanup.sh b/contrib/trials-cleanup.sh
new file mode 100755
index 0000000..2ad8c93
--- /dev/null
+++ b/contrib/trials-cleanup.sh
@@ -0,0 +1,30 @@
+#!/bin/sh
+# Remove all but the N newest test run dirs (that have been started)
+
+trial_rx_dir="$1"
+trial_prep_dir="$2"
+if [ -z "$trial_rx_dir" ]; then
+	trial_rx_dir="/var/tmp/osmo-gsm-tester"
+fi
+if [ -z "$trial_prep_dir" ]; then
+	trial_prep_dir="/var/tmp/prep-osmo-gsm-tester"
+fi
+
+mkdir -p "$trial_prep_dir"
+
+rm_trial() {
+	trial_dir="$1"
+	trial_name="$(basename "$trial_dir")"
+	echo "Removing: $(ls -ld "$trial_dir")"
+	# ensure atomic removal, so that the gsm-tester doesn't take it as a
+	# newly added dir (can happen when the 'SEEN' marker is removed first).
+	mv "$trial_dir" "$trial_prep_dir/"
+	rm -rf "$trial_prep_dir/$trial_name"
+}
+
+# keep the N newest test session dirs that have been started: find all that
+# have been started sorted by time, then discard all but the N newest ones.
+
+for seen in $(ls -1t "$trial_rx_dir"/*/SEEN | tail -n +31); do
+	rm_trial "$(dirname "$seen")"
+done