Find you synchronization level for the system tree (if the whole system tree is synced this will be My Organisation level of the System Tree).
System Tree > Group Details tab look at the Synchronization type by clicking edit.
Towards the bottom of your LDAP Synchronization settings you will find:
Set the 'Delete the systems from the System Tree' setting for when Systems are deleted from the synchronization point (Active Directory).
Thanks for the response.
I've just checked these settings and it turns out that its already enabled, so not sure why its not working 100%.
That makes it a bit more intriguing...
Out of interest how often are you synchronizing/what's the schedule on the server task for AD sync?
Obviously systems will only be removed from the system tree, once a system is removed from AD and this synchronization task runs.
We doe a sync twice a day, once in morning and the other in the afternoon.
I've logged a ticket with support but still to hear back :/