The penis of a stallion or gelding is washed to remove smegma and other dirt or debris. Generally, a gelding would have his penis and prepuce cleaned once or twice a year. The normal penile skin harbors a number of commensal bacteria which are considered non-pathogenic. Overgrowth of specific organisms such as Pseudomonas aeruginosa or Klebsiella pneumoniae on the male external genitalia may result in venereal transmission of the organisms to mares. Routine washing of the stallion's penis with antiseptic soaps should be avoided as it may remove normal non-pathogenic microbial flora which could be replaced by other more pathogenic bacteria. Warm clean water should be used for routine cleansing of the penis. The chapter discusses the step by step procedure for washing the penis with illustrations, and the equipment and supplies needed. It also discusses the necessary conditions for washing the penis.