Background: The site of dystonia onset is known to affect the risk of spread in primary adult-onset focal dystonia, but other factors possibly influencing spread are unknown. This study explored the relationship between age and spread of dystonia in primary adult-onset focal dystonia. Methods: Two survival models analyzed spread of dystonia in a large cohort of patients with primary blepharospasm (BSP) and cervical dystonia. The first model was based on time interval between onset and spread of dystonia, and the second model was based on age at spread. Results: Patients presenting with BSP had a 2-fold higher rate of spread than those presenting with cervical dystonia, regardless of the survival model used. However, survival analysis, based on age at spread, showed that spread develops at a similar age period in both groups, with most spread events occurring after the age of 50. Conclusions: The convergent age of spread in BSP and cervical dystonia is a novel finding indicating age as a factor modulating spread of dystonia. These findings may assist in informing prognostication for patients with primary adult-onset focal dystonia. (c) 2012 Movement Disorder Society