The testis can go for a twist inside the sac it is held. This results in loss of blood supply. If left untreated for more than 6 hours the testis loses function. Typical presentation is a 14 year old boy who develops severe pain, red ness and swelling of the sac of testis suddenly. It is very tender to touch. It is necessary to do a surgery immediately. There is no point in wasting crucial time on different tests. Surgery is diagnostic and also curative; if blood supply returns after untwisting the testis is preserved. If the blood supply is lost the testis may have to be removed. In either case opposite testis has to be fixed to prevent twisting on that side.