Aplasia cutis congenita (ACC) is a heterogeneous group of disorders whose common characteristic is focal absence of skin. In the majority of instances this is limited to the scalp, although other areas of the body may also be involved. Other congenital malformations have been reported to occur with ACC; limb defects appear to be a specific association. Given our experience with ACC, we suggest a classification based on genetically distinct entities. Type I ACC is limited to the scalp. Type II involves body or scalp; IIA involves body or limb defects. Type III is limited to the scalp or limbs. Type IV is associated with epidermolysis bullosa; type IVA is Bart syndrome. Although most reported cases have been sporadic, there are many familial occurrences of all types of ACC. Most published pedigrees are consistent with autosomal dominant inheritance with reduced penetrance, or autosomal recessive inheritance. Careful examination of family members of affected individuals is warranted.