Previous research supports the fear-avoidance model in explaining the transition from acute to chromic non-specific musculoskeletal pain. However, there is still little knowledge on when this vicious circle of pain, disability, pain catastrophizing and fear of movement starts. We performed a daily diary study in 42 patients with acute whiplash injury. Pain, disability, pain catastrophizing and fear of movement were measured on a daily basis with paper diaries for 21 consecutive days. Most participants showed a decline in pain and disability from day 1 to day 21 and this was paralleled by a decline in the fear of movement and pain catastrophizing. Multilevel analyses shoed that both between and within persons, high levels of pain catastrophizing and fear of movement are associated with more pain and disability. Moreover, the fear of movement was also predictive of pain and disability on the following day. We also examined the reverse association, that is, whether the changess in pain predict changes in the next day's fear of movement and pain catastrophizing. Although for the fear of movement the model reached significance, the amount of explained variance was negligibel. In conclusion, this study provides evidence that already in the early stages of whiplash-related complaints, significant associations between fear of movement and pain intensity and disability occur, and that this association may be predictive of the persistence of pain.