This study tested the effect of issuing return-to-activity advice on activity intentions at Day 2 and Day 10 days post simulated mild traumatic brain injury. One hundred and twenty-eight volunteers were randomly allocated to one of two groups who received (n ¼ 65) or did not receive standardized post-injury advice (n ¼ 63). To prime the simulation, the participants read a mild traumatic brain injury vignette about a person who is concussed while playing sport. Then the participants role-played the injured person and reported activity intentions for three activity types (cognitive, physical and restful) twice, once for each time frame (i.e. Day 2 and Day 10). The advice was to rest for the first 24-48 h and then gradually resume normal activities. There was no significant group by activity-type interaction (p > .05) at Day 2. When both time frames were considered, there was no significant group  time frame interaction for any activity type or any item, except for an increase in non-manual (clerical) work and weight training at Day 10 compared to Day 2 in the group with the advice. In general, the intentions for all activity types were consistent with the recovery advice (i.e., rest then increasing activity), even when the advice was not given. However, at Day 10, cognitive and physical activity levels were still expected to be lower than usual (pre-injury), and many participants were uncertain about the concept of cognitive rest. These factors, along with individual patient circumstances, should be taken into account in rehabilitation planning.