Measurement of bone mineral density (BMD) with central dual-energy X-ray absorptiometry (DXA) is the current "gold standard" for diagnosing osteoporosis and for monitoring patients. Errors in demographic information, improper patient positioning, incorrect scan analysis, and mistakes in interpretation can all lead to a wrong clinical decision or action. This paper reviews the fundamentals of positioning, scan analysis, and interpretation for central DXA and highlights some of the common pitfalls that may lead to erroneous results.