Objective structured clinical examination (OSCE) is a reliable, objective and reproducible method of summative assessment of clinical competence. The aim of this study is to evaluate the reliability of OSCE for summative evaluation of final year medical students in both Internal Medicine and Surgery. This was a retrospective cross-sectional study of summative assessment of final-year medical students in Internal Medicine and Surgery at College of Medicine, Enugu State University of Science and Technology. The students’ clinical competence was tested by OSCE. The OSCE consisted of two parts. The A part (picture OSCE, replacing traditional short cases) in which questions were given to students from slide shows. The B part (clinical OSCE, replacing traditional long case) consisted of clinical OSCE stations to test students’ ability and skills in history taking, physical examination, counselling/communication skills, ability to make diagnosis, interpretation of laboratory/radiological results and ability to manage common medical emergencies and conditions. The students' scores in the picture OSCE, clinical OSCE, and final total clinical score scores in both Internal Medicine and Surgery were collated and subjected to analysis with SPSS version 25 (IBM; SPSS, Chicago, IL, USA). Correlation was assessed by Pearson correlation, mean scores compared with paired t-test, reliability assessed by calculating Cronbach's alpha. Statistical significance was considered as p <0.05. A total of 120 students sat for the examinations. There were significant positive correlations between students’ score in Surgery clinical OSCE and Internal Medicine clinical OSCE, r =0.617 (p=0.000); students’ scores in Surgery picture OSCE and Internal Medicine Picture OSCE, r=0.647 (p=0.000); and students’ scores in Surgery clinical examinations and Internal Medicine clinical examinations, r= 0.750 (p=0.000). The reliability of Surgery clinical examinations was 0.851 while the reliability of Internal Medicine clinical examinations was 0.816. OSCE is a more reliable tool than traditional method for the summative assessment of final year medical students. OSCE gives a higher correlation coefficient and Cronbach alpha than the traditional method of assessment.