Background Psychopathy is a clinical condition that describes individuals who are believed to contribute disproportionately to violent crimes and criminal recidivism. The understanding of psychopathy and its presence in Nigerian prison populations is limited. Information on psychopathy in prisoners has almost entirely been based on research in Western countries and it is uncertain whether these research findings are applicable to other settings like Nigeria. Few studies have been done on substance use disorders in prisoners in Nigeria but not in the South-Eastern part of the country. Studies of comparable samples of the convicted and remand prisoners, both within and outside Nigeria, are rare. Aim The aim of this study was to determine and compare the prevalence of psychopathy and substance use disorders among convicted and remand inmates of Enugu prison. Method This was a cross-sectional study that recruited 110 convicted inmates with a matched systematically selected sample of 110 remand inmates. Following ethical approval, consenting prison inmates were recruited into the study. Data collection was undertaken by means of confidentially conducted interview in which a number of suitably translated instruments were administered to the participants. The instruments utilized for the study included a self-developed socio-demographic questionnaire, the Psychopathy Checklist-Revised, the Alcohol Use Disorders Identification Test, the Drug Abuse Screening Test (version 10), and the alcohol and substance use modules of the Mini-International Neuropyschiatric Interview. Results The prevalence of psychopathy in the convicted participants was 8.3% compared with 6.5% among the remand group. Also, the prevalence of substance use disorders was 57.3% in the convicted against 49.1% in the remand group. Nicotine was the most commonly used substance (rate of 44.1%), followed by cannabis (26.4%), cocaine (1.4%) and heroin (0.9%). The majority (87.5%) of those identified as psychopaths had co-morbid substance use disorders. Among the respondents, those with psychopathy committed more violent offences, had relatively more severe sentences (for the convicts), and had a relatively higher record of recidivism than the non-psychopaths. Conclusion The prevalence of psychopathy in the sample is similar to the findings of previous studies (especially those outside North America) and it is associated with the commission of violent crimes and criminal recidivism. Similarly, the prevalence of substance use disorders in the study is similar to the findings of previous studies in Nigeria. There appeared to be a strong comorbidity between psychopathy and the existence of substance use disorder and both conditions were associated with the commission of violent crimes, recidivism and a longer stay in the prison. Psychopathy appeared to accentuate the effects of substance use disorders on criminal involvement. Further studies (both cross-sectional and longitudinal), preferably using larger samples and multiple prison sites, are required to clearly delineate the influence of sociodemographic variables on the occurrence of both psychopathy and substance use disorders in Nigeria. Keywords: Psychopathy, substance use disorders