The adverse events of the nitrogen-containing bisphosphonates are reviewed. Oral bisphosphonates (alendronate, risedronate and ibandronate), mainly used for the treatment of osteoporosis, have been associated with adverse events from the upper gastrointestinal tract, acute phase response, hypocalcaemia and secondary hyperparathyroidism, musculoskeletal pain, osteonecrosis of the jaw and ocular events. Intravenous bisphosphonates (pamidronate, ibandronate and zoledronic acid), used in oncology and for the treatment of osteoporosis, have been associated with all the above adverse events, except those from the upper gastrointestinal tract. Moreover, pamidronate and zoledronic acid have been associated with renal toxicity. Association of bisphosphonates with atrial fibrillation and atypical fractures of the femoral diaphysis remains uncertain. There are a few case reports relating bisphosphonates to cutaneous reactions, oral ulcerations, hepatitis and esophageal cancer. Generally, intravenous are more potent than oral bisphosphonates and the frequency and severity of some of the bisphosphonate- associated adverse events are dose and potency dependent.