Fibromyalgia is a pain disorder associated with frequent comorbid mood, anxiety, and sleep disorders. Despite the frequent use of a complex, poly-drug pharmacotherapy, treatment for fibromyalgia is of limited efficacy. Oxytocin has been reported to reduce the severity of pain, anxiety, and depression, and improve the quality of sleep, suggesting that it may be useful to treat fibromyalgia. To evaluate this hypothesis, 14 women affected by fibromyalgia and comorbid disorders, assuming a complex pharmacotherapy, were enrolled in a double-blind, crossover, randomized trial to receive oxytocin and placebo nasal spray daily for 3 weeks for each treatment. Order of treatment (placebo-oxytocin or oxytocin-placebo) was randomly assigned. Patients were visited once a week. At each visit, the following instruments were administered: an adverse drug reaction record card, Visual Analog Scale of Pain Intensity, Spielberger State Anxiety Inventory, Zung Self-rating Depression Scale, and SF-12. Women self-registered painkiller assumption, pain severity, and quality of sleep in a diary. Unlikely, oxytocin nasal spray (80 IU a day) did not induce positive therapeutic effects but resulted to be safe, devoid of toxicity, and easy to handle.