Mutilation and theft in libraries is a menace that has persisted, and the worsening state of libraries in Nigeria appears to have aggravated its intensity and the consequent detrimental impact. Using a structured questionnaire administered to undergraduate students of Obafemi Awolowo University, Nigeria and a stratified focus group discussion (FGD), information was elicited on their perception of the methods of theft, attitudes to and perceived implications of theft on academic performance and library use. The results reveal that insensitivity to the need of other users, high cost of books, non-detection of previous acts of theft and frequent power outage are some of the factors responsible for mutilation and theft of library materials. It was also revealed that students are aware that mutilation and theft prevent effective use of the library, deprive users of vital information, including from recommended texts, and hence impact negatively on the academic life of the users.