In an open label study, we administered riluzole (50 mg twice a day) to nine patients with genetically confirmed Huntington's disease (HD) (clinical stages 1-3; mean age 46.4 (SD 9.3) years; mean disease duration 8 (SD 3.3) years). The study was designed to evaluate (1) safety and tolerability of riluzole and (2) effects of riluzole on motor impairment, functional disability, cognitive impairment, and behavioral abnormalities using the Unified HD Rating Scale. Patients were evaluated at baseline and after three and twelve months of riluzole therapy. Laboratory tests (hematology and liver enzymes) were repeated monthly. All adverse experiences, reported spontaneously or observed directly by the investigator, were recorded. Riluzole was well tolerated. No increase of serum liver enzymes was seen throughout the study in all but one patient showing a mild elevation. At three months, mean total motor scale (TMS), mean TMS chorea subscore, and mean total functional capacity scale were significantly improved compared with baseline. At twelve months, however, this beneficial effect on motor status and overall function was not sustained. In contrast, severity and frequency of behavioral dysfunction as well as psychomotor speed assessed by the symbol digit modalities test were improved compared with baseline. Our data suggest that there are transient antichoreatic effects and more sustained effects of riluzole on psychomotor speed and behavior in patients with HD. A double-blind, placebo-controlled trial appears highly warranted to establish definitely the symptomatic versus neuroprotective actions of riluzole in HD.