WHAT THIS PAPER ADDSThis observational research demonstrates quantitatively that near infrared illumination increases the visualisation of the subcutaneous venous network between 2.6 and 16.2 times vs. the traditional system of visual inspection. Morphological details of the superficial venous network of the lower extremities are more clearly displayed than with the naked eye, which allows for future studies to be designed to obtain better knowledge of the superficial venous network. This could be of help in understanding the behaviour in both control limbs (CEAP C 0A class) and limbs with venous incompetence (classes C 0S and C 1 of the CEAP classification).Objective: The subcutaneous venous network (SVN) is difficult to see with the naked eye. Near infrared illumination (NIr-I) claims to improve this. The aims of this observational study were to investigate whether there are differences between the different methods; to quantify the length and diameter of SVNs; and to confirm if they differ between C 0A and C 1 CEAP limbs. Methods: In total, 4 796 images, half of them from the visible spectrum (VS) and the other half from the nearninfrared spectrum (NIrS), belonging to 109 females (C 0A : n ¼ 50; C 1 CEAP: n ¼ 59) were used to establish the morphological characteristics of the SVN by visual analysis. With Photoshop CS4, SVN diameters and lengths were obtained by digital analysis of 3 052 images, once the images of whole extremities were excluded. Results: On NIr-I, the diameters, trajectories, and colouration of SVNs of C 1 limbs appeared more irregular than SVNs of C 0A limbs. Compared with the VS images, NIr-I allowed visualisation of a greater length of the SVN in both groups (p < .010). This capacity varied from 2.6 AE 0.9 times (C 1 ) to 16.2 AE 11.9 (C 0A ). While the SVN length seen in the VS images from C 1 limbs was greater than observed in C 0A limbs (p < .001), differences between NIr-I images only existed in the lateral part of the lower leg (p ¼ .016). With NIr-I, the median diameter of the C 1 CEAP SVN veins was 5.8 mm (interquartile range [IQR] 4.3e7.5 mm), while the median diameter in C 0A SVN limbs was 2.6 mm (IQR 2.0e3.6 mm) (p < .001). Conclusion:The NIr-I reveals the characteristics of the SVN better than the naked eye. Further studies are required to determine the significance of the changes in the SVN in C 0A and C 1 limbs, and the factors causing them.