Objective: Premenstrual dysphoric disorder (PMDD) is a severe form of premenstrual syndrome (PMS) that was categorized as a mood disorder in the most recent version of the Diagnostic and Statistical Manual for Mental Disorders. In addition to a history of PMS, a PMDD diagnosis requires prospective symptom assessment for 2 consecutive months. Although the effects of some oxidants-antioxidants were previously studied in PMS, their possible effects in PMDD remain unknown. Paraoxonase-1 is a new high-density lipoprotein-associated enzyme with many antioxidative effects. We hypothesized that assessing serum total oxidant-antioxidant and paraoxonase-1 (PON-1) levels could clarify the role of oxidant/antioxidant system in PMDD. Methods: All participants (n=50) were assessed by an experienced psychiatrist for PMDD by using the Diagnostic and Statistical Manual for Mental Disorders-IV (DSM-IV), Premenstrual Assessment Form and Daily Record of Severity of Problems-Short Form (DRSP) or possible psychiatric disorders including depression, anxiety, and sleep disorders. Serum estrogen, progesterone, total oxidant-antioxidant, and PON-1 levels were measured in the serum of 20 participants with PMDD and 30 asymptomatic controls during the follicular and luteal phases of two consecutive menstrual cycles. Sleep quality, depression, and anxiety symptoms were assessed with the Pittsburg Sleep Quality Index (PSQI), Hamilton Depression Rating Scale (HDRS), and Hamilton Anxiety Rating Scale (HARS), respectively. Results: There were no significant intergroup differences in estrogen, progesterone, oxidant-antioxidant, or PON-1 levels or PSQI scores. However, the mean HDRS and HARS scores were statistically significantly higher for patients with PMDD than for controls. Levels of estrogen, progesterone, and total oxidant-antioxidant were not correlated with HDRS, HARS, or PSQI scores. Conclusions: Considering the lack of differences in hormonal and biochemical levels between the two groups, it may be more efficient and discriminative to longitudinally assess biochemical and cellular stressrelated parameters in subjects with PMDD.Key words: estrogen, progesterone, oxidant, antioxidant, paraoxonase-1, premenstrual dysphoric disorder