Despite its frequency, many, aspects of mild traumatic brain injury (MTBI) remain controversial. This likely reflects the inherent complexities of MTBI and its sequelae as well as various methodological issues in the literature. To further complicate matters, our understanding of what constitutes "necessary" and "sufficient" force to sustain a brain injury, remains limited, particularly in cases of nonimpact brain injury. Little debate exists regarding acute MTBI effects and postconcussional symptoms, although the issue of residual neuropsychological impairment remains hotly contested in many cases. Base rates of neuropsychological "impairment" must be considered in the context of individuals who present for evaluation following possible TBI or MTBI. In this article we highlight some of the critical issues in the assessment and diagnosis of MTBI, including the pitfalls of false-positive and false-negative diagnostic and interpretive errors.