Several studies indicate that patients with multiple sclerosis (MS) have low serum levels of the endogenous antioxidant uric acid (UA), although it has not been established whether UA is primarily deficient or secondarily reduced due to its peroxynitrite scavenging activity. We measured serum urate levels in 124 MS patients and 124 age- and sex-matched controls with other neurological diseases. In addition, we compared UA levels when MS patients were stratified according to disease activity (by means of clinical examination and MRI), duration, disability and course. MS patients had significantly lower serum urate levels than controls (p= 0.001). However, UA levels did not significantly correlate with disease activity, duration, disability or course. Our study favors the view that reduced UA in MS is a primary, constitutive loss of protection against oxidative agents, which deserves further pathogenetic elucidation aimed at future therapeutic strategies.