Red blood cell distribution width (RDW) is a hematological parameter that has been studied in several clinical settings and has been found to be related to both anemia and inflammatory status. As obesity is related to increased inflammatory pattern, we aimed to analyze the RDW in this setting.We determined hematological and inflammatory parameters in morbidly obese patients before bariatric surgery (n=142) and normo-weight controls (n=144).RDW was higher in patients than in controls (p<0.001), along with C-reactive protein (p<0.001) and fibrinogen, (p<0.001) while hemoglobin (p=0.026), serum iron (p<0.001), MCH (p=0.002) and MCHC (p<0.001) were lower in morbidly obese patients. The logistic correlation analysis revealed that only low serum iron (<62 μg/dL) and MCH (<28.14 pg) levels were associated with RDW>14% (OR 7.61, 95% CI: 1.93-30.04, p=0.004; OR 5.67, 95% CI: 1.98-16.24, p=0.001; respectively).These data indicate that the elevated RDW in morbidly obese patients reflects a mild red blood cell hypochromia that does not relate to inflammatory parameters, but to hyposideremia and, consequently, to lower erythrocyte indices, possibly as a result of being on a very low-calorie diet before bariatric surgery. Therefore, RDW should not be considered as an inflammatory marker in this clinical setting.