Objectives: To give a brief, introductory overview of current developments and trends in miniaturized medical sensors which will be informative to non-specialists in the field. Methods: Summary of the different types of wearable and implantable sensors with examples of current state-of-the-art devices and systems used in medical applications. Results: After more than a decade of intensive research and development around the world, miniaturized medical sensors are becoming commercially available, allowing increasingly rapid collection of large-scale medical data and its wireless transmission to health care centers. However, most sensor systems are not yet in routine use and still restricted to specialized sites, undergoing validation trials, mostly within research laboratories. Conclusions: Challenges to routine adoption of medical sensor systems often arise from a combination of lack of awareness of the technology among many medical practitioners, technological limitations of the device systems (artifacts and noise resulting from problems in garment fit or device implantation), and open issues of evaluation and validation for the very broad scope of conditions in home-care and ambient environments over which medical sensors need to operate for routine, reliable, practical use.