Alopecia areata is a chronic inflammatory non-scarring condition affecting the hair follicle that leads to hair loss ranging from small well defined patches to complete loss of all body hair. In about 80% of affected individuals there is spontaneous regrowth within a year. It can present at any age, although 60% of patients develop their first episode of hair loss before the age of 20. There is a family history of alopecia areata in 20% of cases indicative of a genetic basis. A positive family history is prognostic of troublesome alopecia areata, as are onset in childhood, ophiasis (involvement of the scalp hair margins), nail changes and concurrent atopic disease. However, the severity of hair loss at presentation appears to be the strongest predictor of long-term outcome. There is an association with autoimmune diseases, including vitiligo, diabetes, pernicious anaemia and thyroid disease, suggesting that alopecia areata itself is an autoimmune disease, although this is still unproven. Alopecia areata normally presents with hair loss in discrete, well circumscribed patches, which may be small (<1 cm) to very large. Close examination of the periphery of a lesion with a magnifying glass will often reveal short hairs which taper in diameter from their tip to the point at which they emerge from the skin. These 'exclamation mark' hairs are diagnostic of alopecia areata. Individuals with alopecia areata should be referred for dermatological advice if there is diagnostic uncertainty, they have extensive hair loss, they are suffering severe psychological distress or they would like a wig.