OBJECTIVE: Positive occipital sharp transients of sleep (POSTS) are considered a normal variant seen in non-REM sleep; their asymmetrical presentation and relationship with EEG abnormalities have received scarce attention to date. We analyzed these features in a large prospective EEG recordings' sample. METHODS: In this case-control study, over 6 months we collected consecutive patients showing POSTS on their EEG. They were matched with consecutive control subjects (two for each). Demographical data, asymmetries for POSTS and alpha activity, and lateralized or diffuse occurrence of EEG abnormalities (slowing, epileptiform transients) were compared among these two groups. RESULTS: Out of 1254 EEG studies, 102 (8%) patients showed POSTS. They were younger (p=0.031), and more likely to show EEG abnormalities (p=0.008) - including epileptiform transients (p=0.002) - than controls. However, this relationship was influenced by age and recording length. Thirty nine POSTS recordings (38%) had a consistent amplitude asymmetry, but this was not associated with specific EEG abnormalities or alpha asymmetry. CONCLUSION: POSTS are a normal EEG variant, occurring in less than 10% of unselected EEG recordings, mostly in younger adults, without gender predominance. Amplitude asymmetries are found in over one third of subjects. SIGNIFICANCE: POSTS asymmetry, as opposed to other sleep transients, should be considered as normal.