This paper corrects and updates a paper published in BJPsych Open 2018 Mental Health in UK Biobank (https://doi.org/10.1192/bjo.2018.12) that was voluntarily retracted following the finding of errors in the coding of the variable for alcohol use disorder. Notably, the percentage of participants reaching threshold for alcohol use disorder on the Alcohol Use Disorder Identification Tool increased from 7% to 21%. This paper includes corrections and updates. Background: UK Biobank is a well-characterised cohort of over 500,000 participants that offers unique opportunities to investigate multiple diseases and risk factors. An online mental health questionnaire completed by UK Biobank participants expands the potential for research into mental disorders. Methods: An expert working group designed the questionnaire, using established measures where possible, and consulting with a service user group regarding acceptability. Operational criteria were agreed for defining likely disorder and risk states, including lifetime depression, mania/hypomania, generalised anxiety disorder, unusual experiences and self-harm, and current post-traumatic stress and alcohol use disorders. Results: 157,366 completed online questionnaires were available by August 2017. Comparison of self-reported diagnosed mental disorder with a contemporary study shows a similar prevalence, despite respondents being of higher average socioeconomic status. Lifetime depression was the most common finding in 24% of participants (37,434), with current alcohol use disorder criteria met by 21% (32,602), while other criteria were met by less than 8% of the participants. There was extensive comorbidity among the syndromes. Mental disorders were associated with a high neuroticism score, adverse life events and long-term illness; addiction and bipolar affective disorder in particular were associated with measures of deprivation. Conclusions: The questionnaire represents a very large mental health survey in itself, and the results presented here show high face validity, although caution is needed due to selection bias. Built into UK Biobank, these data intersect with other health data to offer unparalleled potential for crosscutting biomedical research involving mental health.