Background/Aims: Recent studies suggest that antecedent disease could impact the pathophysiology of the motoneuron disease Amyotrophic Lateral Sclerosis (ALS). We performed a case-control study to examine the prevalence of 11 antecedent diseases in ALS. Methods: Prevalence of antecedent disease in a 1,288 patient ALS population (Emory University ALS Clinic, Atlanta, Ga., USA) is compared to an age, gender, and geography-matched 7,561 subject control population using a statistical odds ratio (OR) with 95% confidence interval. Results: Association of ALS with odds of arthritis (OR = 0.14); non-ALS neurological disease (OR = 0.14); liver disease (OR = 0.19); chronic obstructive pulmonary disorder or COPD (OR = 0.23); kidney disease (OR = 0.32); adult asthma (OR = 0.39); diabetes (OR = 0.47); hypertension (OR = 0.56); obesity (OR = 0.6); hyperlipidemia or hypercholesterolemia (OR = 0.62); and thyroid disease (OR = 0.78). Conclusions: The prevalence of antecedent disease was overall less in the ALS population. We present two potential lines of inquiry to explain these results: (1) ‘Other disease as ALS protection' - antecedent diseases infer biochemical neuroprotection to ALS; (2) ‘ALS as other disease protection' - the underpinnings of ALS could infer protection to other diseases, possibly via the mechanism hypervigilant regulation or ‘too-high' regulatory feedback gains.