Although the data we reviewed are somewhat inconsistent in terms of the role of STAT3 in events involved in bone remodelling and osteoporosis, most evidence supports a positive effect of STAT3 on both osteogenesis and osteoclastogenesis in vivo, as cell-specific deficiency in either osteoblastic or osteoclastic linage cells impaired differentiation or even cell function. This evidence concerns the gene STAT3 and osteoporosis.