Background. We investigated, for the first time, whether there are any sex differences in retrospective self-reported childhood maltreatment (CM) in Italian adult patients with major depressive disorder (MDD) or bipolar disorder (BD). Furthermore, the potential impacts of patients’ age on the CM self-report was investigated. Methods. This retrospective, cross-sectional study used the data documented in the electronic medical records of patients who were hospitalized for a 4-week psychiatric rehabilitation program. The CM was assessed using the 28-item Childhood Trauma Questionnaire (CTQ), which evaluates emotional, physical, and sexual abuse, as well as emotional and physical neglect. The linear and logistic regression models were used (α = 0.01). Results. Three hundred thirty five patients with MDD (255 women and 80 men) and 168 with BD (97 women and 71 men) were included. In both samples, considerable CM rates were identified, but no statistically significant sex differences were detected in the variety of CTQ-based CM aspects. There was a significant association, with no sex differences, between the increasing patients’ age and a decreasing burden of CM. Conclusion. Both women and men with MDD or BD experienced a similar and considerable CM burden. Our findings support the routine CM assessment in psychiatric clinical practice.