BACKGROUND The morphological changes occurring during the dynamic process of menstruation have previously been described only in terms of data derived from static sources, including histological and electron microscopic studies. Recent advances in pressure-controlled, continuous flow hysteroscopy permit dynamic images to complement the traditional modalities.METHODS A prospective observational study of 15 women (age range 22–52 years) during various phases of active menstrual shedding and repair using the novel hysteroscopic plus histological and scanning electron microscopic approaches. The women had not taken hormonal therapy in the previous 2 months and all had regular menstrual cycles of 27–30 days.RESULTS For the first time, the hysteroscopic appearance of the endometrium during menstruation has been documented. This technique indicates that endometrial loss and regeneration are piecemeal processes that occur simultaneously in different areas of the uterine cavity. The exposed basalis endometrium is rapidly covered with a fibrinous mesh, upon and within which new surface epithelial cells develop. New epithelial cells appeared to arise from the underlying stromal cells rather than as epithelial outgrowths from the residual gland stumps as had previously been thought.CONCLUSIONS Endometrial surface epithelial regeneration is a rapid, localized and piecemeal process that appears to occur as a consequence of cellular differentiation from stromal cells within the residual basalis.