Disrupted nighttime sleep is one of the pentad of symptoms defining Narcolepsy. 
REM sleep behavior disorder (RBD) largely contributes to night sleep disruption 
and narcolepsy is the most common cause of secondary RBD. However, RBD linked to 
narcolepsy (N-RBD) has been insufficiently characterized, leaving unsolved a 
number of issues. Indeed, it is still debated whether N-RBD is an intrinsic 
feature of narcolepsy, as indubitable for cataplexy, and therefore strictly 
linked to the cerebrospinal fluid hypocretin-1 (CSF hcrt-1) deficiency, or an 
associated feature, with a still unclear pathophysiology. The current review 
aims at rendering a comprehensive state-of-the-art of N-RBD, highlighting the 
open and unsettled topics. RBD reportedly affects 30-60% of patients with 
Narcolepsy type 1 (NT1), but it may be seen also in Narcolepsy type 2 (NT2). 
When compared to idiopathic/isolated RBD (iRBD), N-RBD has been reported to be 
characterized by less energetic and quieter episode, which however occur with 
the same probability in the first and the second part of the night and sometime 
even subcontinuously. N-RBD patients are generally younger than those with iRBD. 
N-RBD has been putatively linked to wake-sleep instability due to CSF hcrt-1 
deficiency, but this latter by itself cannot explain completely the phenomenon 
as N-RBD has not been universally linked to low CSF hcrt-1 levels and it may be 
observed also in NT2. Therefore, other factors may probably play a role and 
further studies are needed to clarify this issue. In addition, therapeutic 
options have been poorly investigated.