An `in situ' holographic technique, based on the use of a flexible miniaturized endoscope (diameter less than 1 mm) has been developed for medical applications. The holographic process provides quantitative information on the 3-D geometry of the observed scene, including deformations and movements. The holographic system presented here is based on the use of a multimode fiber bundle (MMB) as a recording medium for the endoscopic holograms. The hologram is obtained by the interference between the light reflected by the object and a reference beam travelling back along the axis of the MMB. The interferogram, sampled on the MMB tip, is then treated electronically. The image is reconstructed numerically.