Background: By magnifying the scalp and structure of hair, trichoscopy enables easy differentiation among various hair loss diseases. Objective: To measure the frequency of representative trichoscopic findings in outpatients with androgenetic alopecia and alopecia areata and the frequency of various trichoscopic findings depending on the disease severity of androgenetic alopecia. Methods: This cross-sectional study included 87 patients with androgenetic alopecia (n=57) and alopecia areata (n=30) treated over a year (2014∼2015). Three dermatologists assessed the trichoscopic findings (hair shaft, hair follicle opening, and perifollicular epidermis) in these patients. Results: Vellus hair was observed in 21 of the 30 patients (70%) with alopecia areata and 20 of the 57 patients (35%) with androgenetic alopecia. Among the patients with androgenetic alopecia, as the disease severity increased, the portion of patients with vellus hair, thickness heterogeneity, and honeycomb pigmentation also increased (p＜0.05). Conclusion: Trichoscopy is very useful for the diagnosis of androgenetic alopecia and alopecia areata. Additionally, the severity of androgenetic alopecia can be assessed using trichoscopy. (Korean J Dermatol 2016;54(9):699∼705)