Background. Information on adverse events (AEs) in hospitalised patients in developing countries is scanty. Objective. To compare the magnitude and characteristics of inpatient AEs in a tertiary, not-for-profit healthcare facility in Kenya, using medical records review and incident reporting. Methods. Estimation of prevalence was done using incidents reported in 2010 from a random sample of medical records for hospital admissions. Nurse reviewers used 18 screening criteria, followed by physician reviewers to confirm occurrence. An AE was defined as an unexpected clinical event (UE) associated with death, disability or prolonged hospitalisation not explained by the disease condition. The kappa statistic was used to estimate inter-rater agreement, and analysis was done using logistic regression. Results. The study identified 53 UEs from 2 000 randomly selected medical records and 33 reported UEs from 23 026 admissions in the index year. The prevalences of AEs from medical records review and incident reports were 1.4% (95% confidence interval (CI) 0.9 - 2.0) and 0.03% (95% CI 0.012 - 0.063), respectively. Compared with incident reporting, review of medical records identified more disability (13.2% v. 0%; p=0.03) and prolonged hospital stays (43.4% v. 18.2%; p=0.02). Conclusions. Review of medical records is preferable to incident reporting in determining the prevalence of AEs in health facilities with limited inpatient quality improvement experience. Further research is needed to determine whether staff education and a positive culture change through promotion of non-punitive UE reporting or a combination of approaches would improve the comprehensiveness of AE reporting.