The serum uric acid (UA) levels were measured in 112 patients with multiple sclerosis (MS) and 794 patients with different types of other neurological diseases (OND) or healthy control group. Serum UA levels, along with relevant clinical parameters of MS and OND, were also investigated. MS patients had significantly lower UA levels than those with transient ischemia attack (344.6 +/- 130.6 micromol/L, P = 0.000), cerebral hemorrhage (311.9 +/- 104.7 micromol/L, P = 0.000), cerebral infarction (291.3 +/- 101.6 micromol/L, P = 0.014) and the healthy control group (312.1 +/- 92.8 micromol/L, P = 0.000). MS patients had significantly higher serum UA levels than those with cryptococcus meningitis or meningoencephalitis (178.9 +/- 107.0 micromol/L, P = 0.000) and tuberculous meningitis or meningoencephalitis patients (175.7 +/- 99.9 micromol/L, P = 0.000). There were no significant differences in UA levels between patients with MS and those with facial neuritis, viral meningitis or encephalitis, pulmonary tuberculosis, polymyositis or dermatomyositis, myasthenia gravis, subarachnoid hemorrhage, migraine, Guillain-Barre syndrome and myelitis. In addition, UA levels were independently correlated with gender and duration of MS, but neither with MRI activity, disability nor subtypes of the disease in MS patients. Our data suggest that UA has two biphasic functions: neuroprotective and injurious. Our studies may help physicians to deal with conditions having abnormal UA levels.