Lavender foal syndrome (LFS), also called coat color dilution lethal (CCDL), is an autosomal recessive genetic disease that affects newborn foals of certain Arabian horse bloodlines. Affected LFS foals have severe neurological abnormalities, cannot stand, and require euthanasia shortly after birth. The popular name originates due to a diluted color of the foals coat, that in some cases appears to have a purple or lavender hue. However, not all foals possess the lavender coat colour, colouring can range from silver to light chestnut to a pale pink. Carrier horses have no clinical signs and DNA testing can determine if a horse carries the gene.

Lavender foal syndrome is thought to be created by an autosomal recessive gene. When a horse is heterozygous for the gene, it is a carrier, but healthy and has no clinical signs of the condition. If two carriers are bred together, however, classic Mendelian genetics indicate a 25% chance of any given mating producing a homozygous foal, hence affected by the disease. Carrier horses can be bred and produce non-affected foals, as long as they are bred with a non-carrier for the LFS gene. It is hypothesized, though untested, that LFS may be linked to another genetic disease that affects Egyptian-related Arabians, juvenile epilepsy. This theory has been raised because of a small number of horses that have produced both LFS and epileptic foals.

LFS is one of six genetic diseases known to affect horses of Arabian bloodlines. Genetic diseases affect other horse breeds, including different coat color-based lethals, such as lethal white syndrome. In addition, the color white in horses, when created by certain alleles of "dominant white" (W), may possibly be fatal if homozygous.