The World Health Organization (WHO) has included complex post-traumatic stress disorder (C-PTSD) in the final draft of the 11th edition of the International Statistical Classification of Diseases and Related Health Problems (ICD-11), which was published in June, 2018 and is scheduled to be submitted to WHO’s World Health Assembly for official endorsement in 2019. Mental health providers will want to be informed about this diagnosis in order to provide effective treatment. Complex PTSD, or developmental PTSD as it is also called, refers to the constellation of symptoms that may result from prolonged, chronic exposure to traumatic experiences, especially in childhood, as opposed to PTSD which is more typically associated with a discrete traumatic incident or set of traumatic events. Although it has been a controversial diagnosis and is not included in the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), lines of evidence support its distinct profile and utility. In this case study, we elucidate and discuss some aspects of the diagnosis and its treatment.