Abstract The current study aimed to examine whether the APOE ε4 allele, associated with dementia with Lewy bodies (DLB), and possibly with dementia in Parkinson’s disease (PD), is also associated ...with idiopathic REM sleep behavior disorder (RBD). Two SNPs, rs429358 and rs7412, were genotyped in RBD patients (n=480) and in controls (n=823). APOE ε4 allele frequency was 0.14 among RBD patients and 0.13 among controls (OR=1.11, 95% CI 0.88-1.40, p =0.41). APOE ε4 allele frequencies were similar in those who converted to DLB (0.14) and those who converted to PD (0.12) or multiple system atrophy (0.14, p =1.0). The APOE ε4 allele is neither a risk factor for RBD nor it is associated with conversion from RBD to DLB or other synucleinopathies.