To evaluate the effectiveness and tolerability of omega-3 polyunsaturated fatty acid (PUFA) supplementation for treatment of trait anxiety among adolescent females with restrictive anorexia nervosa (AN). A pilot double-blind, placebo-controlled randomized trial of adolescent females with AN (N = 24) entering Partial Hospitalization Program (PHP) from January 2015 to February 2016. Participants were randomized to four daily PUFA (2,120 mg eicosapentaenoic acid/600 mg docosohexaenoic acid) or placebo capsules for 12 weeks. A 9-item questionnaire of side effect frequency assessed medication tolerability. The Beck Anxiety Inventory-Trait measured anxiety at baseline, 6, and 12 weeks. Linear mixed models evaluated associations between randomization group and study outcomes. Twenty-two and 18 participants completed 6 and 12 weeks of data collection, respectively. Medication side effect scores were low and were not significantly different between randomization groups at Week 6 (p = .20) or 12 (p = .41). Mean trait anxiety score significantly (p < .01) decreased from baseline to 12 weeks in both groups, and the rate of change over the course of time did not differ between omega-3 PUFA and placebo groups (p = .55). Omega-3 PUFA supplementation was well tolerated in adolescent females with AN. Although power to detect differences was limited, we found no evidence that omega-3 PUFA benefited anxiety beyond nutritional restoration.