Objective: Sleep duration the night before preseason testing can affect baseline symptoms, but the interaction between neurodevelopmental disorders and less sleep is unknown. We examined the relationship between sleep duration, Attention-Deficit/Hyperactivity Disorder (ADHD), and baseline symptom reporting in student athletes. Method: From a baseline database of 30,771 athletes ages 13–18 who had not sustained a concussion in the past 6 months and completed all sections of ImPACT®, including the number of hours slept the night before, 21,866 denied having developmental/health conditions (controls) and 1,029 reported only having ADHD (total sample: age M = 15.4, SD = 1.3; 47.4% girls). Athletes completed the Post-Concussion Symptom Scale within ImPACT®. Athletes were divided into four groups based on their sleep duration the night before testing (≤5, 5.5–6.5, 7–8.5, and ≥9 hours). Mann-Whitney U-Tests were used to compare baseline symptom reporting between athletes with ADHD and controls, stratified by sex and sleep duration. Results: Athletes with ADHD reported greater symptom severity than controls when matched on sex and sleep duration (all ps < .05). Effect sizes between ADHD/Control groups were greater for girls than boys. In athletes who slept 5 or fewer hours, 93% of girls and 49% of boys with ADHD reported having a symptom burden resembling an ICD-10 diagnosis of postconcussional syndrome, compared to 49% of girls and 33% of boys without any comorbidities (girls: χ2(1) = 11.08, p = .002; boys: χ2 = 3.89, p = .049). Conclusions: Poor sleep and ADHD, in combination, confound baseline concussion-like symptom reporting. It may be important to consider the effects of preexisting health conditions, sex, and sleep duration when interpreting baseline symptoms.