The application of nanotechnology to biomedical research is expected to have a major impact leading to the development of new types of diagnostic and therapeutic tools. One focus in nanobiotechnology is to develop safe and efficient drug/gene delivery vehicles. Research into the rational delivery and targeting of pharmaceutical, therapeutic and diagnostic agents is at the forefront of projects in nanomedicine. Silica, as a major and natural component of sand and glass, is a versatile material due to the variety of available chemical and physical modifications that are available, and recently have been widely applied in nanobiotechnology as drug/gene carriers or fluorescent nano-probes. The goal of this brief review is to illustrate selected examples of various functionalized silica nanoparticles as drug/gene delivery systems that have been applied to the arenas of human disease therapy or detection (molecular and cellular imaging).