Clinical studies are very dynamic in nature. This poses a great challenge in building an adaptable informatics platform to support evolving clinical research needs. Center for Information Technology (CIT) at the National Institutes of Health (NIH), in collaboration with the National Institute of Neurological Disorders and Stroke (NINDS), has developed a web-based Clinical Study Information System (CSIS) to support efficient management of clinical data that would improve the quality and timeliness of conducting clinical research. CSIS allows Principal Investigators(PI) to design new electronic Case Report Forms(eCRF) using a Form Designer. A patient registry module enables the study coordinators to recruit and screen new subjects. Most importantly, an ad-hoc query engine allows investigators to stratify patient groups and export data by specifying arbitrarily complex criteria without having to learn database syntax.