The age of first sex has significantly reduced generally in the modern society, particularly Nigeria. Youths often dare the consequences of premarital sex to fulfil sexual desire which in most cases have dire effects on their health, education and social lives. This study investigated possible causes of premarital sex among youths as perceived by lecturers of University of Ilorin, Nigeria. The descriptive survey method was used for the study while a total of 160 respondents were purposively selected. The t-test statistical analysis was used to test the stated null hypotheses at 0.05 level of significance. The measure of central tendency statistics was adopted to determine answers to the research questions. The results revealed that, personal reason was the most perceived reason for premarital sex among youths while inadequate knowledge of reproductive health was perceived as the most important specific factor. Respondents were similar in their perception based on gender and academic ranks. It was recommended that counsellors and health educators should endeavour to provide adequate information to youths on reproductive health and appropriate relationship with friends.