OBJECTIVE: To document neurocognitive and neurobehavioral consequences of 1 versus 2 concussions. DESIGN AND SETTING: Nonequivalent, pretest-posttest cohort design with multiple dependent measures. Participants were selected from a large sample of athletes who participated in a comprehensive, multiuniversity study of football-related concussion. SUBJECTS: College football players who sustained 1 and 2 grade 1 concussive injuries were matched for age, education, and duration of competitive football. MEASUREMENTS: Neuropsychological tests and symptoms checklists. RESULTS: Multivariate analysis of variance did not show a statistically significant difference in test performance between players with 1 or 2 concussions. Chi square analyses revealed that concussions significantly increased the number of symptom complaints, but symptoms returned to baseline by 10 days postinjury. The effects of 2 injuries did not appear to be significantly greater than that of a single injury. Differences in response to concussion were observed. CONCLUSIONS: Neurocognitive and neurobehavioral consequences of 2 concussions did not appear to be significantly different from those of 1 concussion, but methodologic issues place limitations on data interpretation. Additional studies are needed to clarify the neuropsychological consequences of multiple concussions.