Endoanal ultrasound (EAUS) is used in the assessment of the anal sphincter in patients with faecal incontinence. However, interpretation is very operator dependent. 3D technology allows capture of the image of the whole anal canal in three dimensions and manipulation of the image by others not carrying out the scan reducing operator dependence.The aim of the study was to determine whether inter-observer agreement is better using 3D technology compared with 2D images.Material and methods. For the first part of the study inter-observer variability was compared using a small number of patients and a large number of interpreters. Study images of ten randomly selected patients undergoing endoanal ultrasound for faecal incontinence were obtained in 2D format and using 3D technology. Images were interpreted by 4 specialists (defined as personnel who regularly reported scans) and 9 non-specialists with an interest in coloproctology (1 radiologist and 8 colorectal surgeons). For the second part of the study images of forty patients were randomly selected in both formats and interpreted by only 2 specialists. Each image was graded as normal, showing internal sphincter injury, external sphincter injury or a combination.Results. There appeared to be minimal to no advantage for the 3D format over the 2D format for any of the groups in terms of inter-observer variability. For interpretation of the 10 images as expected the inter-observer agreement was low for the non-specialist group (k = 0.11 for 2D and k = 0.16 for 3D) but was surprisingly only moderate for the specialists alone (k = 0.42 for 2D and k = 0.44 for 3D). In the second part of the study there was a higher overall agreement and a slight improvement in interobserver variability with the 3D format. Agreement was moderate for 2D and substantial for 3D (k = 0.60 and k = 0.67 respectively).Conclusions. Despite the ability to view the whole anal canal in different planes, the 3D technology appears to only slightly improve inter-observer agreement and only in expert hands.