Psychometric characteristics of the Postconcussion Symptom Inventory (PCSI) were examined in both concussed (n= 633) and uninjured (n= 1,273) 5 to 18 year olds. Parent- and self-report forms were created with developmentally appropriate wording and content. Factor analyses identified physical, cognitive, emotional, and sleep factors; that did not load strongly or discriminate between groups were eliminated. Internal consistency was strong for the total scales (α = 0.8–0.9). Test–retest reliability for the self-report forms was moderate to strong (intraclass coeffecients, ICCs = 0.65–0.89). Parent and self-report concordance was moderate (r = .44–.65), underscoring the importance of both perspectives. Convergent validity with another symptom measure was good (r = .8). Classification analyses indicated greater discriminability from parent report, but caveats to this are presented. With strong psychometric characteristics, the four versions of the PCSI capture important postconcussion symptoms and can be utilized to track recovery from pediatric concussion and guide treatment recommendations.