ObjectivesAmyotrophic lateral sclerosis (ALS) is a rapidly progressive neurodegenerative disorder. Sleep disturbance may interfere with clearance of abnormal proteins that aggregate in neurodegenerative diseases. The objective of this study was to examine the association between benign prostatic hyperplasia (BPH), a common disorder causing nocturia and sleep disturbance, and risk of ALS and other motor neuron disease (MND). We hypothesised that men with BPH, in comparison to men in the general population, would be at increased risk.DesignThis is a nationwide, population-based cohort study.SettingThis study was conducted among the population of Denmark.ParticipantsWe used linked Danish medical databases to identify all men with a first-time diagnosis of BPH between 1 January 1980 and 30 November 2013 and no prior diagnosis of MND (BPH cohort, n=223 131) and an age-matched general population comparison cohort of men without BPH or MND (n=1 115 642).Primary outcome measureThe primary outcome is diagnosis of MND after the BPH diagnosis (index) date, with follow-up until MND diagnosis, emigration, death or 30 November 2013.ResultsWe used Cox regression to compute adjusted HR, comparing men with and without BPH. After 34 years of follow-up, there were 227 cases of MND in the BPH cohort (incidence rate 0.13/1000 person-years) and 1094 MND cases in the comparison cohort (0.12/1000 person-years; HR 1.05, 95% CI 0.90 to 1.22). Risk did not vary by follow-up time.ConclusionsBPH is not associated with an increased risk of ALS and other MND. Future studies should examine the relation between other disorders that disrupt sleep and MND risk in men and women.