This study investigated the effects of student absenteeism and truancy on academic performance in three selected JHS schools in the Oforikrom Sub-Metropolis. The study adopted the mixed research approach to gather and analyse relevant data; which involved both quantitative and qualitative approaches. The total number of respondents were fifty (50) students who exhibit absenteeism and truancy behaviours, two (2) head teachers and five (5) teachers from the Aprade, Weweso and Anwomaso Basic Schools. All respondents were purposively sampled based on their knowledge on the phenomenon studied. The study found that about fifteen (15) factors resulted in the absenteeism and truancy behaviours of students. The highest factor was the attitude of teachers (poor engagement in learning in classroom). Other included illness, ignorance, family problems, economic hardships, poor head teacher-student relationship, poor attitude towards absence, negative school atmosphere, adaptation to school, and individual reasons, among others. The study also found that the academic performance of such students was low. The study further showed a decreasing performance of students who exhibit absenteeism and truancy with an average grade of 30 for the 2017/2018 academic year. Chi-square test to establish whether there is an association between absenteeism and truancy behaviours of students and academic showed a statistically significant association between academic performance of students and absenteeism and truancy behaviours with a computed Chi-square statistic value of 4.437 with (Asymp.) and p-value of 0.035. Based on the findings, the study recommended the need for effective cooperation between family of victims and schools to address such behaviours. Also, the study suggested that elective courses should be varied depending on the interests and needs of students and suitable environments for these courses should be prepared at schools.