Undetected diabetes (UD) worsens prognosis, increases healthcare costs and reduces productivity in the long term. However, its determinants have not been previously explored in developing countries. In this paper, we assess the determinants of UD in Colombia. We conducted logistic regression analyses using the 2007 Colombian National Health Survey. Taking into account undetected cases (individuals with fasting glucose tests ≥ 126 mg/dL reporting no previous diabetes diagnosis), we found a diabetes prevalence of 5% in Colombia, where 1/3 are undetected cases. Undetected individuals are as likely as detected diabetics to visit a physician during the last 12 months. Despite we found no differences in prevalence between urban and rural settings, diagnoses rates were lower in the later, challenging traditional conceptions on urban diabetes and supporting the hypothesis of a supply-side issue driving undetected diabetes in Colombia. We discuss UD in Colombia using a supply-demand framework. These lessons may be extrapolated to other Latin American countries where policymakers will find them useful to improve diabetes screening activities.