Temporal triangular alopecia, also referred as congenital triangular alopecia, is an uncommon dermatosis of unknown etiology. It is characterized by a non-scarring, circumscribed alopecia often located unilaterally in the frontotemporal region. It usually emerges at ages 2-9 years. Alopecia areata is the main differential diagnosis, especially in atypical cases. Dermoscopy is a noninvasive procedure that helps distinguish temporal triangular alopecia from aloepecia areata. Such procedure prevents invasive diagnostic methods as well as ineffective treatments.

Costello syndrome (CS) is a rare genetic disorder, first described by Costello in 1971, caused by mutations in the HRAS proto-oncogene. Clinical findings include facial dysmorphism, skin disorders, cognitive impairment, cardiac and musculoskeletal defects. There is an increased risk of malignancies in these patients, due to the proto-oncogene mutation, and also sudden death secondary to heart disease. We report a case with characteristic phenotype, highlighting the peculiar skin changes.