Pallidal deep brain stimulation (DBS) is currently the most effective treatment for advanced, medically refractory dystonia. However, factors predicting clinical outcome are not well defined. We reviewed the clinical records of 39 consecutive patients with medically refractory primary dystonia who underwent pallidal DBS implants. Thirty-five patients were implanted bilaterally and four unilaterally. Seven patients had fixed skeletal deformities (FSD). The Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS) scores at baseline, 3 and 12 months after DBS were used to evaluate clinical outcome. We investigated the outcome predictive role of several demographic and clinical factors. FSD patients had a significantly inferior outcome at 12 months, mostly affected by axial scores. All other patients (n = 32) showed a remarkable improvement (median BFMDRS percentage improvement = 87.8). Only disease duration showed a significant correlation with DBS outcome at 3 and 12 months. No other demographic and baseline clinical features predicted DBS outcome. This study confirms that patients with primary, medically refractory dystonia are generally outstanding candidates for pallidal DBS, with the possible exception of axial FSD. Patients with shorter duration of disease may expect a better general outcome. No particular predictive value should be assigned to age at onset, age at surgery, severity of disease, DYT1 status and the presence of phasic or tonic involuntary movements.