This paper aims to evaluate the utility of a single glucometer fasting capillary blood glucose (FCBG) measurement in determining the prevalence of diabetes mellitus in a homogeneous adult population. FCBG measurements were compared with results of the oral glucose tolerance test (OGTT) in 445 subjects aged 30-65 years in an urban cross-sectional study in Old Ramallah. Prevalence of diabetes, sensitivity, specificity and predictive values were calculated at different cut-off levels of FCBG, using OGTT as the reference. The prevalence of OGTT-diagnosed diabetes was 2.7%, while it varied considerably using different cut-off levels of FCBG. The sensitivity of a single glucometer (Exac Tech II) measurement of FCBG at the cut-off level of 6.7 mmol 1(-1) was 33.3%, with a specificity of 98.8%. Using the cut-off level of 6.1 mmol 1(-1) as suggested by the 1998 provisional report of a WHO consultation, the sensitivity increased to 41.7%. At a cut-off level of 5.6 mmol 1(-1), a sensitivity of 66.6% was reached, but the specificity decreased slightly. It can be concluded that a single glucometer measurement of FCBG in an adult population is not useful in determining the prevalence of diabetes mellitus.