BACKGROUND Sporadic Amyotrophic Lateral Sclerosis (sALS) is associated with frontotemporal dementia (ALS-FTD) or milder deficits of cognitive (predominantly executive) dysfunction (ALSCi) in some patients. Some forms of familial ALS (FALS) have a family history of FTD, ALS-FTD, or both, but there have been few reports of ALS-FTD in FALS patients with mutations of the gene superoxide dismutase-1 (SOD1 FALS). The aim of this study was to test the hypothesis that ALSCi may be found in non-SOD1 FALS, but that SOD1 FALS patients would show little or no evidence of cognitive change. METHODS A neuropsychological test battery was administered to 41 SALS patients, 35 control participants, 7 FALS patients with a SOD1 mutation (SOD1 FALS) and 10 FALS patients without a SOD1 mutation (non-SOD1 FALS). RESULTS Relative to control participants, non-SOD1 FALS patients had impaired performance on written verbal fluency and confrontation naming, and reported higher levels of executive behavioural problems. These deficits were absent in SOD1 FALS patients. SALS patients performed poorer than controls only on the Graded Naming Test. All ALS groups had higher levels of behavioural apathy and emotional lability than were found in control participants. Cognitive domains of memory, receptive language, and visuospatial perception were spared. Groups were matched for age, gender, premorbid full-scale IQ, anxiety and depression. CONCLUSIONS Individuals with SOD1 gene mutations are less likely to have significant cognitive changes compared to non-SOD1 FALS patients. Cognitive abnormalities in ALS are heterogeneous and may reflect underlying genetic variations rather than a simple spectrum of extra-motor involvement.