Hemihypertrophy is an overgrowth of a region of the body. In complex or total hemihypertrophy, fully half the body is involved. In other cases, the asymmetry may be limited to single organs, fingers, or other areas of the body such as one leg. In a special form known as hemifacial hyperplasia, half of the face is enlarged when compared to the other half. This condition appears to be congenital in nature, but the causes are not fully understood and it has not been linked with any specific genes.

Infants with hemihypertrophy are usually diagnosed at birth because the asymmetrical nature of the body is usually evident, although the different may be small. As people grow, the hemihypertrophy can become more noticeable. Sometimes hemihypertrophy is not diagnosed until childhood because the variation may be subtle, making it hard to detect at birth. This condition cannot be cured, but there are treatment and management options available.

In people with hemihypertrophy, the larger area may have other differences in addition to size. For example, the skin can be darker, more hairy, prone to acne, or marked with birthmarks. Sometimes the nervous system is involved as well and the patient may also have anomalies in the brain which can lead to intellectual disabilities. People with hemihypertrophy are also at increased risk of some cancers, as well as scoliosis.

Patients with this condition can be monitored for changes. One treatment option is the use of braces to prevent scoliosis and stabilize the body. When the legs are of different lengths, wearing lifts in the shoes is an option, although some doctors may recommend surgery to shorten one limb or lengthen the other. Monitoring for cancers is also an important aspect of treatment so that any malignancies related to the hemihypertrophy can be caught early. Cosmetic surgery may be performed for patients who feel uncomfortable with their appearance.

Each case of hemihypertrophy is slightly different. Some patients experience complications which can make treatment more challenging, while others may be perfectly healthy, except for the colds and flus which everyone gets at various times in life. Treatment must be tailored to the needs of the individual and can involve input from a number of different medical professionals, depending on the specifics of a patient's situation. People with hemihypertrophy may find it helpful to joint support groups and associations so that they can connect with people who also have this rare condition.