Osteoporosis is a disease with continuous loss of bone and, therefore, artificial division into type I and type II (e.g. senile) is not logical. Simple classification of primary and secondary osteoporosis is more practical and useful in their management. Osteoporosis affects ~10% of the World's population, and 3-4% of these patients have treatable secondary causes leading to, or aggravating, this most common metabolic bone disease which is neglected in many instances. We have examined the incidence of secondary causes of bone loss in 1,000 consecutive patients referred to a tertiary osteoporosis referral clinic. 72% of these patients were female, and 90% of these women were postmenopausal. The percentages reported with secondary osteoporosis vary with referral patterns. For example, Francis et al. have reported figures of 20% and 35%, and Mayo Clinic reported figures of 40% and 55% for females and males respectively. Current study shows 46% of females and 75% of males referred to this tertiary osteoporosis clinic had treatable secondary causes of bone loss. Since these reported data are from highly selected populations, the true incidence of secondary causes leading to osteoporosis in the community is likely to be much lower. Table : Incidence of secondary causes of osteoporosis (numbers* and percentages) in 1,000 consecutive patients referred to a tertiary osteoporosis clinic. * Some patients had more than one identifiable/treatable secondary cause. Environmental factors and habits, such as excessive cigarette smoking and/or alcohol abuse, poor diet and other causes leading to osteomalacia (e.g., malabsorption, gastric surgery, drug interference, etc), and various medications especially glucocorticoids lead to bone loss. Other secondary causes include hypogonadism, GnRH therapy, hyperparathyroidism, hyperthyroidism (i.e., sub-clinical or biochemical hyperthyroidism, excessive intake of thyroxin), hypopituitarism, chronic liver disease, myeloma, conditions associated with immobilization and paralysis including hemiplegia. In addition to a good history, physical examination and biochemical markers, non-routine tests such as 24 hour urine calcium; serum intact PTH, 25 (OH) vitamin D, sex-steroid hormone levels are useful in identifying these secondary causes. It is essential to identify and treat the underlying secondary causes aggravating further bone loss prior to embarking on anti-osteoporosis therapy.