Introduction: The Junior Secondary Certificate Examination (JSCE) is a summative examination taken by candidates at the end (the third year) of Junior Secondary Education in Nigeria. The Examination is in two versions--(a) the one being conducted by the States' Ministries of Education (MOE) and (b) the Federal version being conducted by the National Examinations Council (NECO). There was growing concern among stakeholders about the predictive validity of the State version of the JSCE for the Senior Secondary School Certificate Examination (SSCE). The study was undertaken to find out whether there is significant relationship between the overall performance of students in the JSCE and their performance in the Senior School Certificate Examination (SSCE). Method: Schools in Osun State (of Nigeria) constituted the sample for the study. Promotion examination scores of the students in Senior Secondary School (SSS) 1 and SSS 2 as well as their SSCE in six major subjects were compared with corresponding JSCE scores using correlation analysis procedures. Results: These showed that Osun State JSCE is a poor predictor of students' performance in the SSCE. However, JSCE English Language and Mathematics were found to have a greater capacity to predict performance in SSCE English Language and Mathematics than all the other subjects (r = 0.32, p less than 0.05 and r = 0.22 p less than 0.05 respectively). Conclusion: Overall performance in JSCE across the six subjects investigated is a poor predictor of SSCE performance (except English Language and Mathematics). The trend could be due to the constraints facing the MOE which perform the role of an examination body. (Contains 4 tables.)