Urinary tract infections (UTIs) are among the most common bacterial infections. Although comorbid UTI in geriatric patients with delirium or dementia is well known, the prevalence and scope of the association with other neuropsychiatric disorders is unclear. We performed a systematic review of the association between UTIs and delirium, dementia, psychotic disorders, and mood disorders in hospitalized patients. We identified studies by searching PubMed, PsycInfo, and Web of Knowledge, and the reference lists of identified studies and review papers. Seventeen publications met the inclusion criteria. The primary findings were: (1) 88% of publications reported a positive association between UTIs and neuropsychiatric disorders; (2) 47% reported that the clinical course of a neuropsychiatric disorder may be precipitated or exacerbated by a UTI; (3) the mean weighted prevalence of UTIs in subjects was 19.4% for delirium, 11.2% for dementia, 21.7% for nonaffective psychotic disorders, and 17.8% for mood disorders. Our findings, which must be interpreted carefully given the heterogeneity among the studies, suggest that UTIs are highly comorbid in hospitalized patients and may precipitate or exacerbate some neuropsychiatric disorders. The association extends beyond geriatric patients with delirium, affects males and females, and includes adults with psychotic and mood disorders. These findings underscore the important interface between physical and mental health. Potential underlying mechanisms are also reviewed, including complex interactions between the immune system and the brain.