Background: Most individuals recover from a concussion within 7-10 days. However recovery may be very prolonged. Individuals who do not recover within the usual time are said to have postconcussion syndrome (PCS). The objective of this study was to examine the demography and predictors of PCS. Methods: This was a retrospective cohort study of 284 consecutive concussed patients 221 of whom had PCS on the basis of at least three symptoms persisting at least 1 month. A uniform, internationally accepted definition of concussion was used. Results: The 221 cases showed considerable heterogeneity in clinical features of PCS. They averaged 3.3 concussions with a range of 0 to 12+ concussions, and 62.4% occurred during sports and recreation. The median duration of PCS was 7 months at the time of examination, with 11.8% lasting more than 2 years. Surprisingly, 23.1% with PCS had only 1 concussion. The average age was 27 years (range 10-74). The average number of persistent symptoms was 8.1. 26.2% had a previous psychiatric condition, ADD/ADHD, a learning disability, or previous migraine headaches. The prevalence of arachnoid cysts and Chiari malformation in PCS exceeded the general population. Conclusions: In most of our cases, PCS was disabling, and lasted for months or years.