OBJECT: Sport-related concussions (SRCs) among youth athletes represent a significant public health concern. Prior research suggests that females fare worse symptomatically after an SRC. The authors aimed to assess sex differences in number, severity, and resolution of postconcussive symptoms using reliable change index (RCI) methodology applied to days to return to symptom baseline. METHODS: Between 2009 and 2011, 740 youth athletes completed valid neurocognitive and symptom testing before and after an SRC using Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT). A total of 122 female and 122 male athletes were matched on number of prior concussions, age, and number of days to first postconcussion test. At baseline and postconcussion, the authors compared each of the individual 22 symptoms on ImPACT to calculate individual symptom severity and aggregate symptom severity, or the Total Symptom Score (TSS). When comparing individual symptoms, the significance level for the comparison of each symptom was set at 0.05/22 = 0.0023. When comparing aggregate symptom severity, or TSS, a single value was compared, requiring an alpha set to 0.05. The number of days to return to baseline TSS was compared using RCI methods set at the 80% confidence interval, equal to a raw score point value of 9.18 on the TSS. RESULTS: At baseline, females reported a greater severity for the symptom, “sleeping less than usual,” compared with males (0.88 +/- 1.49 vs 0.31 +/- 0.86, p < 0.001). However, no other individual symptom severity differences were noted before or after SRC. At baseline, females exhibited a statistically significant greater aggregate symptom severity than males (7.24 +/- 10.22 vs 4.10 +/- 6.52, p = 0.005). Greater aggregate symptom severity for females was also found postconcussion (21.38 +/- 19.02 vs 16.80 +/- 17.07, p = 0.049). Females took longer to return to baseline TSS (9.1 +/- 7.1 days vs 7.0 +/- 5.1 days, p = 0.013). CONCLUSIONS: The results of this retrospective study indicate that females endorse a greater severity of symptoms at baseline and postconcussion than males without significantly different symptom profiles. Furthermore, after suffering an SRC, females take longer to return to their baseline symptom level.