Traumatic events increase risk of mental illnesses, but childhood neglect prevalence in psychiatric disorders is understudied. This systematic review and meta-analysis assessed neglect prevalence, including emotional neglect (EN) and physical neglect (PN), among adults with psychiatric disorders. We conducted a systematic search and meta-analysis in 122 studies assessing different psychiatric disorders. Prevalence was 46.6% for unspecified neglect (Ne), 43.1% for EN, and 34.8% for PN. Although a moderating effect of the psychiatric diagnostic category was not confirmed, some clinical diagnoses had significantly lower prevalence rates than others. Patients with bipolar disorder and major depressive disorder showed lower prevalence rates of EN and PN, whereas lower prevalence was found in psychotic disorders and eating disorders for PN only. Neglect assessment was a significant moderator for Ne and PN. No moderating effect of age and sex on neglect prevalence was found. Heterogeneity levels within and between psychiatric diagnostic categories remained high. This is the first meta-analysis examining diverse types of neglect prevalence considering different psychiatric diagnoses. Our results explore the prevalence of childhood neglect and its subtypes among adults with psychiatric disorders, contributing to understanding the nuanced interplay between neglect and specific psychiatric conditions, and guiding interventions for affected individuals.