There is an impression both in clinical practice and in research literature that patients with amyotrophic lateral sclerosis (ALS) possess 'heroic stoicism with a low frequency of depression'. Reliance on specific interview methods may have contributed to differing estimates of mood disorder in people with ALS. The objective of the current study was to compare prevalence rates of depression and anxiety in ALS using different assessment tools. The Beck Depression Inventory (BDI), The Hospital Anxiety and Depression Scale (HADS) and the Spielberger State-Trait Anxiety Inventory (STAI) were sent to a 12-month consecutive sample of 190 patients with ALS attending a tertiary referral clinic in the UK. Data were collected from 104 patients with ALS. Using BDI scores, 44% were categorized as not depressed, 37% were mild-moderately depressed, 13% were moderately-severely depressed, and 6% were severely depressed. In contrast, the HADS depression subscale identified 75% as not depressed, 13% were in the borderline range, and 13% were categorized as meeting 'caseness' for depression. Twenty-five percent of the patients were using antidepressant medication. The estimated prevalence of mood disorder amongst patients with ALS may vary significantly depending on the measure used.