The pituitary gland constitutes, together with the hypothalamus, the regulatory core of the endocrine system. Whether the gland is capable of cell regeneration after injury, in particular when suffered at adult age, is unknown. To investigate the adult pituitary's regenerative capacity and the response of its stem/progenitor cell compartment to damage, we constructed a transgenic mouse model to conditionally destroy pituitary cells. GHCre/iDTR mice express diphtheria toxin (DT) receptor after transcriptional activation by Cre recombinase, which is driven by the GH promoter. Treatment with DT for 3 d leads to gradual GH+ (somatotrope) cell obliteration with a final ablation grade of 80–90% 1 wk later. The stem/progenitor cell-clustering side population promptly expands after injury, concordant with the immediate increase in Sox2+ stem/progenitor cells. In addition, folliculo-stellate cells, previously designated as pituitary stem/progenitor cells and significantly overlapping with Sox2+ cells, also increase in abundance. In situ examination reveals expansion of the Sox2+ marginal-zone niche and appearance of remarkable Sox2+ cells that contain GH. When mice are left after the DT-provoked lesion, GH+ cells considerably regenerate during the following months. Double Sox2+/GH+ cells are observed throughout the regenerative period, suggesting recovery of somatotropes from stem/progenitor cells, as further supported by 5-ethynyl-2′-deoxyuridine (EdU) pulse-chase lineage tracing. In conclusion, our study demonstrates that the adult pituitary gland holds regenerative competence and that tissue repair follows prompt activation and plausible involvement of the stem/progenitor cells.