The Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) has dropped the multiaxial diagnostic system and moved to a dimensional system of diagnostic classification. This change means that there is no longer a separate Axis V or specific diagnostic category for assessment of functioning. In addition, the Global Assessment of Functioning Scale (GAF), the previously endorsed numerical rating scale used for assessment of functioning and reported on Axis V, has been eliminated. In its place, DSM-5 offers psychiatrists a new tool for assessment of global functioning and impairment, the World Health Organization Disability Assessment Schedule 2 (WHODAS 2.0). Any single global assessment of functioning rating scale inevitably has limitations. Nevertheless, the GAF has been widely used in clinical and research settings and has been adopted as meaningful by psychiatric, legal, administrative, and insurance systems and institutions. The changes in DSM-5 in regard to the conceptual and practical assessment of functioning and impairment raise many questions. In this article, I review the implications for forensic psychiatric evaluations of the changes in the recommended assessment of functioning in DSM-5.