The investigator embarked on the research to find out the causes and consequences of cohabitation among university students in Oyo State, South-West Nigeria. In order to carry out the investigation, the researcher formulated two research questions and one hypothesis to guide the investigation. The researcher constructed an instrument known as "Cohabitation Among University Students, Causes and Consequences Questionnaire" (CAUSCCQ) to collect information from the respondents. The investigator carried out a reliability test of the instrument using the test re-test method. A reliability coefficient of 0.85 was obtained showing that the instrument was reliable to carry out the research. The items of the instrument had face and content validity as well as language appropriateness. The researcher used 3 research assistants to administer 271 copies of the instrument on the respondents. The research assistants retrieved 245 copies of the questionnaire. The researcher scored, collated and made use of the mean and standard deviation to answer the two research questions while one-way Analysis Of Variance ANOVA was used to test the hypothesis. The investigation revealed in Table 1 that some students cohabit because of high on-campus accommodation fee, with mean score of 2.79, some others cohabit due to financial difficulties in order to save on rent, food and other expenses and also as a result of their freedom from parental control and supervision. The research found out in Table 2 that one of the consequences of cohabitation is unwanted pregnancy with mean score of 3.52. The investigation also revealed in Table 2 that unwanted pregnancy may result into abortion with mean score of 3.49. Finally, the research found out that there is no significant difference among Federal, State and Private university student cohabiters in their assessment of the consequences of cohabitation. It is therefore recommended that Federal, State and Private owners of universities should put up adequate number of halls of residence for students.