The alignment of lower extremities is an important consideration in many clinical situations, including fracture reduction, high tibia osteotomy, total knee arthroplasty, and deformity correction. Mal-alignment of lower extremities is not only a simple cosmetic problem, but it can also produce pain, limp, and early degenerative arthritis. An assessment of lower extremity alignment, including its location and magnitude of deformity, can be achieved via mal-alignment test and mal-orientation test, using a lower extremity standing full-length radiography. Proper evaluation allows the surgeon to determine an effective treatment plan for deformity correction.