HLA-DQB1 typing was performed in 60 Caucasian subjects with sleepwalking (SW) disorder and their families and 60 ethnically matched subjects without any diagnosed sleep disorder. A total of 21 sleepwalkers (35.0%) were DQB1*0501 positive vs eight (13.3%) controls (P = 0.0056; odds ratio = 3.5, 95% CI = 1.4-8.7). The family data for all HLA subtypes were further assessed for allelic association with SW using the transmission-disequilibrium test. A significant excess transmission was observed for DQB1*05 and *04 alleles in familial cases, strongly suggesting that a DQB1 polymorphic amino acid might be more tightly associated than any single allele. Sequence screening revealed that Ser74 in the second exon shared by all DQB1*05 and *04 was 20 times transmitted against 4 times non-transmitted (P = 0.001) in familial cases of SW. Thus, together with narcolepsy and REM sleep behavior disorder, these findings suggest that specific DQB1 genes are implicated in disorders of motor control during sleep.