The researchers reviewed 30 studies involving 7,993 people to understand whether recovery three months after a mild or moderate traumatic brain injury (TBI) can predict what happens over the following 6–12 months. Most participants had a mild TBI. Overall, symptoms and day-to-day functioning improved most between leaving hospital and three months after injury. However, many people continued to experience symptoms or difficulties beyond three months, with rates ranging from 21% to 65% depending on the study and how recovery was measured. The studies differed too much in their methods and reporting to identify which personal or injury-related factors predict longer-term recovery. Many also excluded potentially vulnerable groups, such as older adults and people with existing cognitive or mental health conditions or intoxication. There was not enough evidence to compare mild and moderate TBI. Further well-designed research that includes a wider range of patients is needed to improve care and better predict recovery.