The significant number of veterans and active military personnel with potential Posttraumatic Stress Disorder (PTSD) makes it important to improve PTSD diagnosis and treatment. A powerful PTSD Clinical Decision Support System (CDSS) based on evidence-based treatment strategies will be useful. To address this critical need, IAI has been awarded a new contract entitled, “A Virtual PTSD Clinical Assistant with Cloud Computing and Mobile Interface: VPCA.” The key innovation of VPCA is using the Hadoop Ecosystem with scalable data storage and processing capability to enable the evidence based clinical decision support empowered by Watson-like predictive analytics across different domains for PTSD patients. VPCA consists of a set of indispensable components grouped in four sub-systems, and supported by a Hadoop storage system, a map reduce engine and standard vocabularies and terminologies of clinical PTSD. The first sub-system is for knowledge and rule authorization, and it transforms the PTSD decision guidelines used by practicing PTSD professionals, into business rules. The second sub-system is for data integration and warehousing in a distributed fashion, including as many clinical data as possible for Watson-like predictive analytics. The third sub-system is for knowledge and rule discovery that can automatically and continuously improve the reasoning potential of the proposed virtual assistant. The data mining algorithms in IAI’s ABMiner and its meta-optimization for model selection will be migrated into the Hadoop Ecosystem. The fourth sub-system is for online clinical decision support. VPCA uses cutting-edge natural language processing technology for clinical data, an open-source clinical decision support platform called OpenCDS, and scalable architecture based on cloud and distributed computation to handle big data. VPCA’s online decision support for diagnostics and treatment will help experienced PTSD clinicians, general practitioners and residents.