Patients with frontal lobe brain damage are reportedly impaired on tasks that require plan development and execution. In this study, we examined the performance of 15 patients diagnosed with frontal lobe dementia and 14 patients with focal frontal lobe lesions on the Tower of London planning task. Patients with frontal lobe dementia committed a significantly higher number of rule violations, made more moves, and demonstrated longer solution time latencies compared to their matched controls. Patients with frontal lobe lesions demonstrated significantly delayed solution times and also made more moves compared to their matched controls. Frontal lobe lesion patient performance suggests an impairment in execution-related processes, while frontal lobe dementia patients appear to be impaired in both plan development and execution. Despite these findings, the identification of a specific cognitive impairment that induces these planning problems remains elusive.