Alopecia areata (AA) is a common, non-scarring, autoimmune hair-loss disorder with a complex genetic and environmental etiology. A higher incidence rate of AA in the female population is well described. It is unclear why females are more likely to be diagnosed with AA and what, if any, differences in disease phenotype exist between males and females. The identification of gender specific characteristics of disease may help clinical management and patient education in cases of AA. Accordingly, we recruited 481 North-American Caucasian AA patients (336 female, 145 male) to assess age of onset, autoimmune and atopic co-morbidity, nail involvement, family history of AA and autoimmune disease, and disease subtype. There was a female predominance (female to male ratio 2.3:1) in this AA study population. We found that male AA patients are more likely to be diagnosed in childhood (age <10 years, P= 0.067) and have a family history of AA (P= 0.004). On the other hand, female AA patients are more likely to be diagnosed in adolescence (age 10-20 years, P= 0.083), have co-morbid nail involvement (P= 0.0257), and have concomitant autoimmune disease (P= 0.014), particularly thyroid disease (P= 0.058). The clinical implications of disease heterogeneity between males and females remains to be determined.