Objective: Summary of the current knowledge of sonographically and clinically detectable anal sphincter injury. Design: Review. Setting: Department of Gynaecology and Obstetrics, Charles University and University Hospital Pilsen. Summary: Review of the current international literature covering the given problem. Occult anal sphincter tear is defined as an injury, which is clinically undetectable and recognizable just on endoanal ultrasonography. Total frequence of anal sphincter defects detected by sonography varies between 19–67%. At any rate majority of them likely seem to be injuries which are clinically detectable, however undiagnosed and missed. Isolated defect of internal anal sphincter is an example of real occult anal sphincter injury. This is found in around 2% of all vaginal deliveries. A diligent digital examination of perineum after the delivery and a proper education of perineal anatomy is the cornerstone in improving of the diagnostics. Endoanal ultrasound may serve as a tool in facilitation of the diagnosis.

        Key words: third degree tear, OASIS, occult anal sphincter injury, anal incontinence, fecal incontinence, pelvic floor, perineal trauma, delivery, endoanal ultrasound, EAUS