Congenital femoral deficiency (CFD) refers to a spectrum of congenital (present at birth) malformations of the thigh bone (femur) due to incomplete or abnormal development. CFD may affect one leg (most commonly) or both legs. Severity can range from minor shortening of the femur (appearing normal), to complete absence of much or all of the femur. Deficiency or instability of the hip and knee joint often are also present and effect treatment options for each person. Various systems for classifying CFD have been proposed. Some experts classify CFD according to radiological appearance, while others classify CFD according to factors that affect options for treatment. The underlying cause of CFD typically is not known, but it does not appear to be inherited. Researchers suspect it is caused by a disruption during early prenatal development, which may occur randomly or as a result of an environmental factor such as infection or trauma. Taking the drug thalidomide during pregnancy can cause CFD and other limb deficiencies in an unborn child. Management of CFD requires a multidisciplinary team of specialists, which may include a pediatric orthopedic surgeon, prosthetist, and physical therapist. The main goal of treatment is to maximize function and mobility. Due to the range of severity and potential abnormalities affecting other bones or joints, there is no single treatment approach that applies to all cases. However, almost all people with CFD will need some combination of non-surgical, surgical, and orthotic treatment. Examples of possible surgical treatment options include reconstruction and limb-lengthening in those with reconstructable hip and knee joints, and amputation and/or rotationplasty for use of a prosthesis.