Glucocorticoids (GCs) have various effects on bone metabolism, which can lead to reduced bone formation [1,2]. Histomorphometric analyses of bone biopsies from GCtreated patients have shown lower bone volume, trabecular/wall/osteoid thickness and mineral apposition rate, and higher resorption parameters versus postmenopausal women [1,2]. As bisphosphonates (BPs) can decrease bone loss in GC-treated patients [3,4], we studied patients from the HORIZON-Glucocorticoid-Induced Osteoporosis (GIO) trial [5] to evaluate the effects of BPs on bone quality, remodelling, morphology, and mineralization. In this 12-month, double-blind study, 833 men and women taking GCs were randomized 1:1 to receive a single iv zoledronic acid 5 mg infusion (ZOL) plus daily oral placebo, or daily oral risedronate 5 mg (RIS) plus a single iv placebo infusion [5]. Transiliac crest bone biopsies were performed on patients agreeing to take part in this substudy. Samples containing the inner and outer cortex, and intact trabecular bone were analyzed. Biopsies from21patients in both treatment groupswere analyzedas a single cohort. Qualitative analysis showed no pathological findings, osteomalacia, marrow dyscrasia/fibrosis, or woven bone. The lamellar structure of newly formed bone was of normal quality. Results of the quantitative histomorphometric analysis are shown in Table 1.