Purpose. To compare the changes in macular sensitivity (microperimetry) and macular thickness with different degrees of diabetic macular edema. methods. Sixty-one eyes of 32 consecutive diabetic patients were included in this cross-sectional study. All included eyes underwent functional and morphologic examination of the macular area. Best corrected visual acuity (ETDRS charts), macular sensitivity, and macular thickness were quantified. Lesion-related macular sensitivity and retinal fixation were investigated with an advanced, automatic microperimeter. Optical coherence tomography (OCT) was used to quantify macular thickness. results. The 61 included eyes were graded, by two retinal specialists, for diabetic macular edema as follows: 16 were graded as no macular edema (NE), 30 as non–clinically significant macular edema (NCSME), and 15 as clinically significant macular edema (CSME). Macular thickness significantly increased from the NE to the CSME group (P < 0.0001), whereas macular sensitivity significantly decreased from the NE to the CSME group (P < 0.0021). A significant correlation coefficient was noted between retinal sensitivity and normalized macular thickness (r = −0.37, P < 0.0001). Linear regression analysis showed a decrease of 0.83 dB (P < 0.0001) for every 10% of deviation of retinal thickness from normal values. Visual acuity and central macular sensitivity correlated significantly in the NCSME group (r = −0.6, P = 0.0008), but not in the NE (r = −0.144, P = 0.6) or in the CSME (r = −0.46, P = 0.11) groups. conclusions. Macular edema may be better documented by adding macular sensitivity mapping by microperimetry to macular thickness measurement by OCT and visual acuity determination because macular sensitivity seems to be a relevant explanatory variable of visual function, independent of macular thickness data. Moreover, microperimetry may be of value in predicting the outcome of diabetic macular edema, because it incorporates a functional measure that may supplement the predictive value of OCT and visual acuity.