OBJECTIVES: The problem of antimicrobial resistance (AMR) has assumed pandemic dimensions especially among low-and middle-income countries such as Nigeria. Irrational use of currently available antimicrobial agents is a major contributory factor. There remains a paucity of documented information on the determinants of antibiotic prescribing among physicians in Nigeria to guide future strategies to reduce AMR. This study therefore aimed to investigate the patterns and determinants of antibiotic prescribing among doctors in a tertiary hospital in Nigeria as the first step to improve future antibiotic use in hospitals. METHODS: A cross-sectional survey of the determinants of antibiotic prescribing among doctors in the Lagos State University Teaching Hospital, Ikeja, was performed using a structured questionnaire. Information was obtained about the doctors and the factors determining their prescription of antibiotics. The results were summarized using descriptive statistics with Statistical Package for Social Science. RESULTS: Ninety-eight respondents were studied with a mean age of 36.24(9.01) years, a mean duration of practice of 10.68(9.25) years, and mainly males (64.3%). Ninety-seven percent prescribe antibiotics frequently, mostly based on clinical judgment and experience with rare laboratory supports. Factors of cost, drug availability, and information from pharmaceutical representatives influenced antibiotic prescribing. There were indications of nonexistence or nonfunctional institutional policies and guidelines regarding antimicrobial therapies. CONCLUSION: There is an urgent need to institute evidence-based institutional policies and guidelines for improving antimicrobial use among hospitals in Nigeria. This is already being followed up.