Alcoholism and other substance abuse continue to be a problem among younger and older populations. The prevalence of substance abuse has only been studied among outpatients and in limited samples of inpatients in Kenya. This study therefore aimed to establish patterns of substance abuse in patients admitted in general medical facilities in Kenya. The Alcohol Use Disorders Identification Test (AUDIT) and the Alcohol, Smoking and Substance Involvement Screening Test (ASSIST) were used to measure the prevalence of substance abuse among patients in 10 medical facilities in Kenya. Data were collected over a 4-week period in November 2005. The overall alcohol user rate using the two instruments was 25.1% and 25.5%, respectively. All the patients who used alcohol exhibited pathological use, which bordered from harmful use to dependence. Apart from alcohol, other abused substances included tobacco, cannabis, cocaine, amphetamines/khat, and sedatives. The clinicians' pick rate for substance use in general hospitals was negligible. These findings suggest the need for specific enquiry for substance abuse in patients in general medical facilities.