Objectives: To describe symptom prevalence and structure after mild traumatic brain injury (MTBI) in a population-based cohort. Methods: Symptoms data were collected at 3 months post-MTBI by use of the Rivermead Post-concussion Symptoms Questionnaire (RPQ) at follow-up of 2602 patients attending 39 Swedish hospitals. Spearmans rank correlation analysis was used to explore correlations between symptoms and structural equation modelling (SEM) was performed by use of several fit indices to explore if data were compatible with one or more factors. Results: Questionnaires were received from 2523 (97%) patients with a mean age of 31 years (median 22, range 6-96). A majority of the respondents (56%) reported no remaining injury related symptoms, 24% reported three or more symptoms and 10% reported seven or more symptoms. All symptoms exhibited strong positive inter-relations and SEM provided strong support for a single or two factor solution. Fit indices were only slightly weaker for three and four factor solutions. Conclusions: A significant minority of patients reported multiple symptoms to persist at 3 months after MTBI. The observed structure of symptoms according to RPQ demonstrates a common factor for all symptoms, but also sub-groups of symptoms as previously suggested.