Orthorexia nervosa (ON) is a recently proposed eating disordered behaviour characterized by an obsessional or exaggerated fixation on healthy eating. The published literature is scarce regarding its classification, clinical presentation, management and long-term outcomes. Herein, we present the clinical and follow-up findings of an 18-year-old woman with ON comorbid with depression, successfully treated with mirtazapine. The patient had a 12-month history of obsessional behaviours for "healthy food", characterized by suppression of sugar and fat from her diet, tightly counted meal calorie content, eating only self-made meals, avoidance of eating in public, unacceptance of other person's opinions on diet, social isolation and a weight loss of 15 kg (body mass index of 16.2 kg/m2). A score of 19-points was initially obtained on the ORTO-15 questionnaire, suggesting the presence of orthorexic tendencies and behaviours. The patient also reported a 1-month history of depressed mood, anxiety, anhedonia, fatigue, insomnia with early morning waking, leading to the presumptive diagnosis of ON with comorbid depression. Treatment with mirtazapine for 11 months resulted in the remission of the disordered eating behaviour, a sustained regain of weight, a score of 41-points on the ORTO-15, and to the resolution of depressive symptomatology (including insomnia). To our knowledge, this is the first description of ON with comorbid depression successfully treated with mirtazapine. This case highlights the possible usefulness of mirtazapine as a treatment option for patients with ON. However, randomized controlled studies are warranted to confirm the current findings.