To compare subfoveal choroidal thickness (GCSF) in patients with diabetic macular oedema (DMO) and healthy subjects using swept source optical coherence tomography (SS-OCT). Cross-sectional study including 50 eyes of 36 patients with DMO, and 47 eyes of 34 patients as a control group. GCSF was measured in both groups, analysing between the eyes with DMO according to the type of oedema (predominantly cystic or diffuse). The study groups were homogeneous in terms of mean age (63.4 years for DMO and 62.65 years for controls; P=.36) and the mean axial length (23.21mm for DME and 23.53mm for controls; P=.06). A statistically significant reduction in the eye with DME GCSF compared to controls (P=.041, 222.9 vs. 192.82 μm) was observed. No statistically significant differences were observed in the eyes with DMO with a predominantly cystic pattern and diffuse oedema (P=.13, 178.68 vs. 205.7 μm). The GCSF in patients with DMO could be reduced. Future studies are needed to confirm these preliminary results. Copyright © 2016 Sociedad Española de Oftalmología. Published by Elsevier España, S.L.U. All rights reserved.