A varicocele is an enlarged, twisted vein (varicose vein) in the scrotum, most often on the left side. It feels like a “bag of worms” and may occasionally cause discomfort.

A large varicocele is thought by some to be related to some cases of abnormally low sperm count. While studies have not shown that varicocele repair has value for improving fertility, some doctors will repair a large varicocele, based on the belief that it may improve a man's abnormally low sperm count. Otherwise, varicoceles are usually left alone.