A large sample of undergraduates (N = 2,326) were screened for general health. The screen discretely included items assessing postconcussion symptomatology and neurologic history. A subsample of experiment-blind participants whose self-reported postconcussion symptom levels were >0.5 SD below the screening sample mean (low symptomatic; n = 45) or >0.5 SD above the screening sample mean (high symptomatic; n = 53) were re-evaluated for postconcussion symptomatology 3 to 90 days later. The sample included 50 participants who reported history of mild head injury (MHI) and 48 controls. MHI was defined as loss of consciousness of ≤20 minutes within the past 10 years, but no more recent than 3 months. Persons with history of >1 head injury or with other neurologic history were not included in the study. The stability of postconcussion symptoms differed by high symptomatic versus low symptomatic presentation (high symptomatic presentation was more variable) and by gender (females were more variable), but not by actual history of MHI. Sex differences in self-reported postconcussion symptomatology are consistent with gender-related differences in reporting of other physical and psychological symptoms. In addition to demonstrating differences in the stability of self-reported postconcussion symptomatology, the current study provides normative test-retest data for the Postconcussion Symptom Checklist for extreme responders by gender and MHI status.