An in situ holographic technique based on the use of a flexible miniaturized endoscope (diameter less than 1 mm) was developed for medical applications. The holographic system features a multicore optical fiber (MCF) coupled to a CCD camera to record the hologram. The hologram is formed by reflection on the tip of the MCF, sampled, and then treated electronically after video acquisition. The image is reconstructed numerically, providing more flexibility to the holographic process. This process required the development of an ad hoc computer algorithm, which was used as well to simulate the whole holographic procedure. The performance of this holographic method was assessed in terms of spatial resolution and sensitivity to noise. The low spatial sampling rate of the MCF was not a limitation for the range of distances investigated (≥ 4 mm). It was predicted to adversely affect the image only at very close observation distances (< 2 mm). The different sources of noise have been analyzed and their relative importance quantified. The resolution proved to be unaltered by noise originating from the propagation of coherent light in the MCF. The miniaturized endoholoscope prototype was capable of resolving 5 μm-objects at a 4 mm distance (the smallest distance reachable with the current setup). This provides the possibility to observe biological tissues at the cellular level. Preliminary investigations in biological conditions have been performed with the holographic system. The observation of an object through a turbid medium was improved by the holographic technique. Images of biological tissues demonstrated the ability to perform coherent imaging of cells, potentially providing major contribution to in vivo and in situ spectroscopic diagnostic capabilities at the microscopic scale.