Abstract Serum and urine selenium levels were determined in patients with diabetes by hydride generation atomic absorption spectrometry. Mean serum selenium concentrations measured in patients with diabetes mellitus (64.9±22.8 μg/l) were significantly lower than those determined in the control group (74.9±27.3 μg/l) ( P<0.05). Mean serum selenium concentrations were not significantly different between the two groups of diabetic patients considered ( P>0.05). Mean urine selenium concentration in diabetic patients (18.8±10.7 μg/l) were not significantly different from those measured in the control group (20.2±10.1 μg/l) ( P>0.05). No significant differences in serum and urine selenium levels were found if related to sex of patients ( P>0.05). Application of linear regression analysis to serum and urine selenium levels and patients' age showed a non-statistically significant correlation ( P>0.05). Given the marked overlap between the two ranges of the populations, the predictive values of serum selenium in diabetic patients are low.