This paper presents a model of chronic pain [Young and Chapman (Pain, affect, nonlinear dynamical systems, and chronic pain: Bringing order to disorder. In G. Young, A. W. Kane, & K. Nicholson (Eds.), Causality of psychological injury: Presenting evidence in court (pp. 197-241). New York: Springer, 2007)]. It includes extensive coverage of the systems perspective. The paper expands the model to medically unexplained symptoms and provides a developmental model of how these may unfold and influence adult presentation after events such as accidents. Similarly, the model is examined for the developmental roots of personality disorder. The paper examines other threats to validity of diagnosis in cases of psychological injury.