Various approaches will make wearable medical systems comfortable for the user: circuit miniaturization is important, but this approach is ideally combined with flexible and/or stretchable integration, in order to obtain conformable, randomly deformable circuitry. Imec’s UTCP process (Ultra-Thin Chip Package) is an enabling technology for flexible packaging and miniaturization. An UTCP consists of chip thinned down to ~25 µm, embedded in spin-on polyimide materials, yielding a <100µm thick flexible package. Since this UTCP technology passed the first feasibility investigation phase, research is now focused on optimizing the UTCP yield and reliability, and to improve the flexibility of the full circuit. Imec is also developing an integration technology to embed electronics into stretchable devices. Such device consists of flexible islands including electronic components, connected with each other through stretchable interconnects. The islands and interconnects are embedded using an elastomer maintaining the stretchability. The reliability of this technology is of major importance, especially during mechanical loading (stretching) of the devices. Based on simulations (Finite Element Modeling) and on extensive reliability testing, various design and process changes are performed to improve the lifetime of these devices. Furthermore, since most wearable systems are using telemetry, we optimize carefully the antenna design and total system assembly towards best antenna performance, since this will lead to less power consumption, enabling a smaller battery contributing also to the miniaturization of the total device. The performance of an antenna is strongly related to its shape and size. All materials and components placed in the vicinity of an antenna however play also an important role in its functionality, and for a wearable device also the presence of the human body has a clear influence. From the start of the device development, when selecting materials and components, antenna simulations and experiments are essential to ensure optimal antenna performance.