Objectives Along with the growth of the elderly population in the world and in Iran, the population of elderly prisoners is also increasing. Issues related to criminals and prisoners, especially their relationship with psychiatric issues, are one of the most challenging and widely used fields of research. More research needs to be conducted in the country's prisons regarding the problems of this age group, especially their mental problems.. This study aimed to compare the personality disorders of elderly offenders in Tehran prisons based on the type of crime in 2023. 
Methods & Materials This cross-sectional study was conducted in 2023 on 274 people over 60 years old in prisons in Tehran. Sampling was done using a systematic random method. The questionnaires used included a demographic characteristics questionnaire and the Millon Clinical Multiaxial Inventory-III (MCMI-III). Data analysis was performed using SPSS software, version 26. Comparisons between qualitative variables were performed using the Chi-square test or Fisher's exact test.
Results Of the 274 people surveyed, 199 (72.6%) had at least one personality disorder. The mean age of the subjects was 65.03±5.163 years. The largest age group participating in the study was men with 86.9%. The lowest prevalence of personality disorder was associated with antisocial personality disorder at 0.4% and the highest prevalence was associated with antisocial personality disorder at 31%. There was significant relationship between the prevalence of histrionic personality disorder in the subjects based on the type of crime (P=0.001, df=7, χ2=43.565). There was also a significant relationship between the prevalence of obsessive personality disorder in the subjects based on the type of crime (P=0.005, df=7, χ2=20.531). In addition, the prevalence of histrionic and obsessive personality disorders was higher in debtors and fraud offenders than in other offenders. 
Conclusion Given the high prevalence of personality disorders in elderly prisoners, and the results obtained from this study, it is recommended that educational measures and early identification of these types of disorders, as well as counseling to modify inappropriate behaviors in these individuals, which will set the stage for future crimes and may lead to recidivism and re-imprisonment after release, be planned and implemented.