The aim of this double-blind and placebo-controlled trial was to investigate whether saffron (stigma of Crocus sativus L.) could relieve symptoms of premenstrual syndrome (PMS). Double-blind, randomised and placebo-controlled trial. Departments of Gynaecology/Obstetrics and Psychiatry, Tehran and Zanjan University of Medical Sciences. Women aged 20-45 years with regular menstrual cycles and experience of PMS symptoms for at least 6 months were eligible for the study. Women were randomly assigned to receive capsule saffron 30 mg/day (15 mg twice a day; morning and evening) (group A) or capsule placebo (twice a day) for a two menstrual cycles (cycles 3 and 4). The primary outcome measure was the Daily Symptom Report, and secondary outcome measure was the Hamilton Depression Rating Scale. In this trial, saffron was found to be effective in relieving symptoms of PMS. A significant difference was observed in efficacy of saffron in cycles 3 and 4 in the Total Premenstrual Daily Symptoms and Hamilton Depression Rating Scale. The results of this study indicate the efficacy of C. sativus L. in the treatment of PMS. However, a tolerable adverse effects profile of saffron may well confirm the application of saffron as an alternative treatment for PMS. These results deserved further investigations.