The purpose of this study was to examine the relationship between postconcussion symptom complaint (PCS) severity and positive coping factors (knowledge, self-efficacy, and attributions) in a sample of individuals who have sustained a mild TBI, above and beyond the demographic and psychiatric predictors that have been most commonly examined. Ninety-one people with a history of reported mild TBI were surveyed. Hierarchical regression analyses revealed that demographic variables and psychiatric symptom severity predicted PCS severity. Consistent with our hypotheses, knowledge, self-efficacy, and attributions, when taken together, made an independent and significant contribution to prediction of PCS severity (21% of additional variance). The most potent factor was attribution, or the extent to which one attributes symptoms to mild TBI versus other causes. Those who attribute their symptoms to TBI are more likely to report greater symptom severity overall. Taken together, knowledge, self-efficacy, and attributions contribute independently to PCS severity. Additional research is needed to determine if these factors are amenable to intervention.