['Limited data are available regarding the prevalence and nature of invalid computerized baseline neurocognitive test data.', 'To identify the prevalence of invalid baselines on the desktop and online versions of ImPACT and to document the  utility of correcting for left-right (L-R) confusion on the desktop version of ImPACT.', 'Cross-sectional study of independent samples of high school (HS) and collegiate athletes who completed the desktop or online versions of ImPACT. Participants or Other Participants:  A total of 3769 HS (desktop = 1617, online = 2152) and 2130 collegiate (desktop = 742, online = 1388) athletes completed preseason baseline assessments.', 'Prevalence of = ImPACT validity indicators, with correction for L-R confusion (reversing left and  right mouse-click responses) on the desktop version, by test version and group. Chi-square analyses were conducted for sex and attentional or learning disorders.', 'At least 1 invalid indicator was present on 11.9% (desktop) versus 6.3% (online) of the HS baselines and  10.2% (desktop) versus 4.1% (online) of collegiate baselines; correcting for L-R confusion (desktop) decreased this overall prevalence to 8.4% (HS) and 7.5% (collegiate). Online Impulse Control scores alone yielded 0.4% (HS) and 0.9% (collegiate) invalid baselines, compared with 9.0% (HS)  and 5.4% (collegiate) on the desktop version; correcting for L-R confusion (desktop) decreased the prevalence of invalid Impulse Control scores to 5.4% (HS) and 2.6% (collegiate). Male athletes and HS athletes with attention deficit or learning disorders who took the online version were more  likely to have at least 1 invalid indicator. Utility of additional invalidity indicators is reported.'] Does prevalence of invalid computerized baseline neurocognitive test result in high school and collegiate athletes?