We present the manufacture and characterisation of a fully 3D printed, low-cost optical microscope using both a 3D printed chassis and 3D printed illumination and imaging optics. The required commercial components, consisting of a basic camera for image acquisition and light emitting diode controlled by a Raspberry Pi for illumination, are integrated into the 3D printed microscope with the full design shown for ease of replication. Our 3D printed microscope uses a single 3D printed objective lens with a 2.9x magnification and a numerical aperture of 0.07. To benchmark the imaging performance of the system, we used standard test targets and histological specimens, namely, a Giemsa-stained blood smear sample and a thin section of mouse kidney stained with Haemotoxylin and Eosin. We demonstrated that sub-cellular resolution was obtained, and we corroborated this by imaging individual red blood cells and intricate anatomical details of the stained mouse kidney section. All of this was achieved using entirely 3D printed hardware and optics, at a fraction of the cost of a commercial brightfield microscope, while presenting remarkable potential for customisation and increased accessibility for diagnostic imaging applications. ### Competing Interest Statement The authors have declared no competing interest.