Over the past ten years, there has been an increasing recognition that syndromes of frontotemporal dysfunction (FTD) are a common occurrence in patients with amyotrophic lateral sclerosis (ALS). Such syndromes may be present in as many as 6% of patients with ALS. Conversely, the occurrence of motor neuron dysfunction in patients with clinically pure frontotemporal dementia is increasingly recognized. This suggests that to some extent there are overlapping...