This read-only counter reports the number of seconds since this specific IS-IS adjacency last transitioned into the 'up' state. It gives an administrator adjacency-level uptime, complementing the circuit-level csIsisCircUpTime, which is useful when a circuit stays up but individual neighbor adjacencies flap independently. For instance, a low csIsisISAdjUpTime value on one neighbor over a multiaccess LAN where other adjacencies show long uptimes would point to a problem specific to that one neighboring router rather than the shared media.