Xeroderma pigmentosum (XP) is a genetic disorder in which there is a decreased ability to repair DNA damage such as that caused by ultraviolet (UV) light. Symptoms may include a severe sunburn after only a few minutes in the sun, freckling in sun-exposed areas, dry skin and changes in skin pigmentation. Nervous system problems, such as hearing loss, poor coordination, loss of intellectual function and seizures, may also occur. Complications include a high risk of skin cancer, with about half having skin cancer by age 10 without preventative efforts, and cataracts. There may be a higher risk of other cancers such as brain cancers.

XP is autosomal recessive, with mutations in at least nine specific genes able to result in the condition. Normally, the damage to DNA which occurs in skin cells from exposure to UV light is repaired by nucleotide excision repair. In people with xeroderma pigmentosum, this damage is not repaired. As more abnormalities form in DNA, cells malfunction and eventually become cancerous or die. Diagnosis is typically suspected based on symptoms and confirmed by genetic testing.

There is no cure for XP. Treatment involves completely avoiding the sun. This includes protective clothing, sunscreen and dark sunglasses when out in the sun. Retinoid creams may help decrease the risk of skin cancer. Vitamin D supplementation is generally required. If skin cancer occurs, it is treated in the usual way. The life expectancy of those with the condition is about 30 years less than normal.

The disease affects about 1 in 100,000 worldwide. By region, it affects about 1 in 370 in India, 1 in 20,000 in Japan, 1 in 250,000 people in the United States and 1 in 430,000 in Europe. It occurs equally commonly in males and females. Xeroderma pigmentosum was first described in the 1870s by Moritz Kaposi. In 1882, Kaposi coined the term xeroderma pigmentosum for the condition, referring to its characteristic dry, pigmented skin. Individuals with the disease have been referred to as "children of the night" or "moon children".