To evaluate the efficacy and tolerability of norethindrone acetate (NA) as single-agent hormonal therapy for suppression of endometriosis symptoms in adolescents and young adults. Retrospective study. Two academic medical centers. A keyword search using the query 'NA' was applied to the electronic medical records of all women treated by one gynecologist (M.R.L.) from 1992 to 2010. IRB-approved chart review was then conducted on the index records. Continuous treatment with NA (5-15 mg daily). Postoperative bleeding and pain scores; adverse effects. One hundred and ninety-four patients with surgically diagnosed endometriosis initiated NA postoperatively during the study period. Median patient age was 18.9 years. 92.2% of patients had stage 1 or 2 disease, and distribution was similar among those excluded. Median pain scores decreased from 5 at NA initiation to 0 at follow-up (P = .0001) and bleeding scores from 2 to 0, respectively (P = .001) for all stages of endometriosis. Post-NA bleeding scores were improved regardless of prior hormonal regimen, and post-NA pain scores improved in all patients except for those previously prescribed GnRH-agonist plus add-back. Most patients (55.2%) did not report any side effects. The most common adverse effect was weight gain (16.1%), with a mean increase in BMI of 1.2 ± 1.6 kg/m(2) at 12 months. NA alone is a well-tolerated, effective option to manage pain and bleeding for all stages of endometriosis. Among those on prior hormonal therapy, symptoms improved after NA initiation.