Caf-au-lait spots are dark spots on the skin that look like birthmarks. Most children have the pigment from birth, and it almost never becomes more extensive. The pattern of the pigment distribution is unique, often starting or ending abruptly at the midline on the abdomen in front or at the spine in back. Most commonly the patches are on the buttocks and lumbosacral back. The patches are usually large, and have irregular borders resembling the "coast of Maine". This is in contrast to the spots of neurofibromatosis, which have a smooth border resembling the "coast of California". They are light to medium brown.

As reflected by the name - which of course means "coffee with milk". They are usually present at birth, but may arise later in the first few years of life. They are much more common in black infants. Caf-au-lait spots range from about about five millimeters to more than several centimeters in Caf-au-lait spots are harmless. CAL spots are caused by an increase in melanin content with the presence of giant melanosomes. A significant increase in melanocyte density is noted in the CAL spots of patients with NF1 compared with patients who have isolated. About 50% of individuals with NF1 have a spontaneous mutation.

The high incidence of new mutations is thought to result from the large size of the gene, which increases the likelihood of spontaneous mutations. CAL spots without NF1 involvement. About 95 percent of people with NF1 have caf-au-lait spots. In fact, birthmarks that could be classified as caf-au-lait spots often show up in people who don't have NF1. A person will only have one or two such birthmarks. CAL spots are more frequently observed in children of African American race. Caf-au-lait spots are usually present at birth, increasing in size and number with age. CAL lesions do not require medical care. Monitoring of associated conditions is required.