Objectives: To evaluate the practice of aminoglycoside use/monitoring in Kenya and explore healthcare worker (HCW) perceptions of aminoglycoside monitoring to identify gaps and opportunities for future improvements, given the low therapeutic index of aminoglycosides. Methods: This was a two-phase study whereby we reviewed patients' medical records at Kenyatta National Hospital (October-December 2016) in Phase 1 and interviewed HCWs face to face in Phase 2. Outcome measures included describing and evaluating the practice of aminoglycoside use and monitoring and compliance to guidelines. Data were analysed using descriptive and inferential analysis. Results: Overall, out of the 2318 patients admitted, 192 patients (8.3%) were prescribed an aminoglycoside, of which 102 (53.1%) had aminoglycoside doses that did not conform to national guidelines. Aminoglycoside-related adverse effects were suspected in 65 (33.9%) patients. Monitoring of aminoglycoside therapy was performed in only 17 (8.9%) patients, with no therapeutic drug monitoring (TDM), attributed mainly to knowledge and skill gaps and lack of resources. Out of the 28 recruited HCWs, 18 (64.3%) needed training in how to perform and interpret TDM results. Conclusions: The practice of using and monitoring aminoglycosides was suboptimal, raising concerns around potential avoidable harm to patients. The identified gaps could form the basis for developing strategies to improve the future use of aminoglycosides, not only in Kenya but also in other countries with similar settings and resources.