Introduction In Sri Lanka, medico-legal work is carried out by specialist and non-specialist government medical practitioners. Therefore, the Forensic Medicine program assumes an important position in the undergraduate medical curriculum. The Objective Structured Practical Examination (OSPE) conducted in the third or fourth year in the undergraduate curriculum of most medical faculties in Sri Lanka is designed to assess practical aspects of key areas in forensic medicine. This study evaluates scores of the OSPE in undergraduates. Methods A selected sample of 515 answer scripts of fourth-year medical students in five consecutive batches from 2009-2013, were evaluated by two authors and the scores analysed. Results The mean scores for injury description were 51.6%, 58% and 59.5% for burns, fractures and basic injuries, respectively. Fifty-seven percent of students demonstrated competence with regard to MLEF and MLR documentation with marked weakness in stating the cause of death. Thirty-eight percent obtained less than 50% for questions related to identification and interpretation of postmortem changes, artefacts, injuries and pathological changes. Thirty-three percent scored less than 50% marks in the medico-legal interpretation of skeletal remains. In the study, more than 50% of students scored more than 80% marks in toxicology. Students obtained an average score of 68% and 51% respectively in the identification of dissecting instruments and dissection techniques. Conclusions The need to strengthen the undergraduate forensic medicine curriculum with close supervision by specialists and training of medical officers prior to engaging in medico-legal work is recommended to prevent gross errors in medicolegal practice.