Mismatch negativity (MMN) is an event –related evoked potential (EP) that reportedly reflects the brain''s detection of differences in acoustic stimuli. It''s clinical use is not routine and the EP itself has questionable reliability. This study measured MMN in response to long-duration tonal stimuli in typically developing children ages 7-13. MMN was present in 7 of the 10 children evaluated. Although MMN may have promise as a tool to assist in the diagnosis and monitoring of individuals with auditory processing abnormalities, as well as those with hearing loss and/or language impairments, the use of MMN as a clinical measurement tool at this time is questionable. These results should assist students and professionals understand more clearly the data collection challenges as well as the reasons MMN is not routinely used clinically today. More studies are needed to establish the reliability of MMN in normal individuals.