The weak performance of university undergraduates currently in Nigeria can be traced to the University admission structure. Applicants who met admission requirements in the Senior Secondary School Certificate by acquiring the requisite five credits or its equivalent are seen as potential University undergraduate students. Candidates who score the required cut off points in the Unified Tertiary Matriculation Examination (UTME) and Post-Unified Tertiary Matriculation Examination (PUTME) are presumed to be proficient of pursuing chosen courses of study effectively in the University. This study investigated the relationship between University Tertiary Matriculation Examination (UTME), assessment and the first-year academic performance of 2016/2017 students in Federal University of Lafia, Nasarawa State, Nigeria. Descriptive survey research was used as the research design to find the analytical predictive legitimacy and validity of University Tertiary Matriculation Examination (UTME) and the students’ academic performance. The population of 1500 students were admitted into the University within the 2016/2017 academic session and a stratified and purposive random sampling technique was used to collect data from a sample of 360 students from selected Departments of the Faculties of Arts, Science and Social Sciences. A self- developed pro-forma invoice was used to collect student’s UTME scores along with Grade Point Average (CGPA) for the first year. A correlation analysis was used to establish the relationship between UTME scores and First session examination results of students. The validity index of the research instrument was determined and two hypotheses were formulated and a regression analysis used to determine the relationship between UTME scores and the CGPA in Federal University of Lafia. While the CGPA was the criterion variable, the UTME scores was the predictor variable. The results revealed that students’ UTME scores do not essentially imply their genuine scores or intellectual ability. This was confirmed by the weak relationships revealed by students’ scores in UTME and the corresponding CGPA at the end of the first year. The study recommends that a more vigorous post-UTME screening to sieve the candidates before the candidates is offered admission. The JAMB also needs to monitor more effectively the examination management process to safeguard any form of manipulations of results given the fact that the computer-based process can also be compromised by desperate stakeholders.