Teriparatide (TPT) (C181H291N55O51S2) represents a recombinant molecule acting as human osteoanabolic agent. Transitory hypercalcemia (TH) has been reported in osteoporotic patients treated with daily TPT. Our purpose is to analyze the biochemical features as well as clinical risk factors for fractures in patients with severe osteoporosis treated with TPT who developed TH during first 12 months. This is an observational real-life study. In patients with TH biochemical blood markers like osteocalcin, CrossLaps and P1NP assessed at one year have statistically significant higher values than in subjects associating serum calcium within normal limits under the drug.