In this paper we introduce the concept of CMOS Body Dust. Body dust, as we envisage is to be, is a swarm of physical micro-sensing systems designed in CMOS as a cube with the size of red blood cells such that they will be drinkable, or directly injectable into specific body parts to deliver vital diagnostic information wirelessly. As such they can identify the source of a disease such as a tumor mass. The aim of this paper is therefore to discuss and introduce the challenges related to design of a CMOS architecture with bio-sensing instrumentation in a small form-factor, to be in the same order of size as red blood cells (e.g a red cells have a diameter of around 7 μm). With such a constraint we aim for a total size of less than 10 μm³ and discuss trade-offs in power and area.