Not only childhood-onset, but also adult-onset primary dystonia may spread to multiple body parts. The relative risk of spread by site of onset of dystonia, important for clinical prognosis and approach, has not been well characterized. The aim of this study was to prospectively follow the spread of dystonia in 132 consecutive patients and to estimate the risk of spread by the site of onset of dystonia. The patients were included in the study if primary focal dystonia was the only sign of neurological disease other than tremor; i.e. in all patients a single body part could be identified as affected at the onset. At the end of the followup (mean duration 7.5 years; range 5.2-13.4 years), 96 patients (73%) remained focal, while 26 (20%) and 10 (7%) progressed to segmental and generalized dystonia, respectively. The highest likelihood for further spread was observed in patients with initial blepharospasm (10 out of 30 patients; 33.3%), followed by dystonia of upper extremities (32.3%), torticollis (19.6%), and laryngeal dystonia (6.7%). In addition to the highest risk for further spread of dystonia, blepharospasm was associated with the fastest rate of spread (the second region affected on average after 1.2 years). Our results demonstrated that the initial site of primary dystonia was relevant for the risk of spread.