To investigate the effect of sulthiame (STM) in West syndrome (WS) an open, uncontrolled add-on study was undertaken during initial pyridoxine (PDX) therapy in 12 infants, two with idiopathic and ten with symptomatic WS. All patients were initially treated with PDX (150-300 mg x kg (-1)body weight day(-1) ). In seven patients (58%) seizures and hypsarrhythmia stopped during the week after introduction of STM (10 mg x kg (-1)body weight day (-1)). In one the positive effect was temporary. Five of the responders (42%) remained seizure-free and without hypsarrhythmia under STM monotherapy, while one developed complex partial seizures after 25 months. STM was most effective in idiopathic WS (2 /2). During treatment with STM medication no patient suffered side effects attributable to the substance. Further controlled studies are necessary to evaluate the benefit of this potentially effective treatment.