Teratozoospermia, also known as teratospermia, is a semen alteration in which there is a large number of spermatozoa with abnormal morphology.It is a sperm condition that may lead to serious consequences, such as male infertility. The sperm parameter that is compromised is sperm morphology. The World Health Organisation (WHO) offers guidelines to evaluate semen parameters (some examples of these parameters are concentration, motility, or morphology). The values set by WHO can be used to determine normality, so if the value of a given semen parameter is below the reference, it may suggest a sperm pathology. With regard to teratozoospermia, the shape of the spermatozoon is assessed. Formerly, teratozoospermia was diagnosed if 14% of the sperm had a normal shape. In 2010, WHO updated its reference values, and now a man only has to meet a 5% rate of properly shaped spermatozoa to be within normality. Therefore, in order to diagnose teratozoospermia by the current standards, a man has to show a high rate of dysfunctional spermatozoa; more than 96% of his spermatozoa have to be morphologically abnormal.