This study aimed to assess planning ability in adults with traumatic brain injury (TBI) using a 4-disk version of the Tower of London (TOL). Thirty three individuals with TBI were compared with equivalent numbers of matched controls. Overall, the TOL4 was shown to be sensitive to the effects of brain injury, with the TBI group performing significantly more poorly on this version of the planning test than the matched controls. More specifically, group differences were found to be related to the complexity of the planning problems, particularly among a TBI subgroup with localised prefrontal damage. Results of the study provide support for the adverse effects of TBI on planning ability, and the important role of the prefrontal cortex in planning.