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.