Background: Trichotillomania (TTM) is a medical condition that involves recurrent and irresistible urges to pull out their own hair. TTM generally follows a chronic course in most patients and is difficult to treat and manage. Recently, N-acetylcysteine (NAC) has shown efficacy in the treatment of TTM. Objective: The purpose of this study was to assess the efficacy of treatment with NAC in trichotillomania children younger than 13 years of age. Methods: We evaluated 15 patients under 13 years old who visited the Department of Dermatology at Chosun University Hospital between 2014 and 2019 for TTM. An initial dose of 400-mg NAC was administered to patients under 8 years and 800 mg to patients older than 8 years old. If there was no improvement for 2 weeks, the dose was increased with the maximum daily being 2,400 mg. Results: The mean age of patients was 10.7 years; 8 were boys and 7 were girls. They presented with several asymptomatic focal patches of hair loss with different hair lengths on scalp. The dermoscopic findings were broken hairs, v-sign hairs, coiled hairs, and focal erythema. 10 out of 15 patients had a good response to NAC, whereas 5 patients did not respond to the treatment. The differences between the 2 groups were the treatment duration and total NAC doses. The effective group had a mean NAC of 973 mg/day for 11.5 weeks, while the non-effective group had a 1060 mg/day dose for 4 weeks. Conclusion: NAC could be an effective and safe treatment option for TTM in children. (Korean J Dermatol 2019;57(10):600∼607)