Although the medical complications of sports are usually traumatic in nature, infectious hazards also arise. While blood-borne pathogens such as HIV, hepatitis B, and hepatitis C, cause significant illness, the risk of acquiring these agents during sporting activities is minimal. Skin infections are more commonplace, arising from a variety of microbial agents including bacterial, fungal, and viral pathogens. Sports involving water contact can lead to enteric infections, eye infections, or disseminated infections such as leptospirosis. Mumps, measles, and influenza are vaccine-preventable diseases that have been transmitted during sporting events, both in players and in spectators. Prevention is the key to many of these infections. Players should be vaccinated and should not participate in sports if their infection can be spread by contact, airborne, or droplet transmission.