Summary Sleep driving is most often classified as a variant of sleepwalking, but should be distinguished from impaired driving due to misuse or abuse of sedative/hypnotic drugs. Z-drugs; zolpidem and zopiclone in particular, have been associated with the majority of reported cases of impaired driving. Numerous studies have found z-drugs in driving under influence (DUI) related police stops, arrests and accidents. Impaired drivers are reported to have 1) blood levels of z-drugs that exceed therapeutic ranges 2) failed to take the medication at the correct time or remain in bed for sufficient time and/or 3) combined z-drugs with other central nervous system (CNS) depressants and/or alcohol. Consistent with CNS depression, z-drug-impaired drivers may demonstrate cognitive function at low levels with drivers still able to understand and respond to questions while sleepwalkers are completely unable to understand or interact with police. Z-drug-impaired drivers are often severely physically impaired, unable to stand up or maintain balance while sleepwalkers are able to stand and walk unaided. Sleep driving and impaired driving due to z-drugs may overlap. Sleep driving and drug-impaired driving are statistically rare events, but due to the billions of doses prescribed each year may still result in numerous DUI related arrests and accidents.