Injuries and poisoning are associated with mental disorders. The association may be stronger if comorbid mental illness is involved. This study explores whether selected mental disorders (stress, anxiety, depression, attention deficit hyperactivity disorder [ADHD], bipolar, obsessive-compulsive disorder [OCD], schizophrenia) are associated with injuries and poisoning and if the presence and frequency of comorbid mental illness affect these associations. Analyses utilize medical claims data for adult employees of a large corporation during 2017–2021. Approximately half or more of the index mental disorders experience comorbid mental illness. Odds of injury and poisoning are significantly greater for each mental disorder and tend to be significantly greater when comorbid mental illness exists (vs. the mental disorder alone), especially for the associations involving poisoning. Schizophrenia alone and in combination with other mental illness has the strongest associations with injury and poisoning. OCD is only associated with injury and poisoning, and ADHD is only associated with poisoning, if accompanied by comorbid mental illness.