Posthitis (pronounced pos-THI-tis) is the inflammation of the foreskin (prepuce) of the human penis. It is characterised by swelling and redness on the skin and it may be accompanied by a smelly discharge.

The term posthitis comes from the Greek "posthe", meaning foreskin, and "-itis", meaning inflammation.

Posthitis can have infectious causes such as bacteria or fungi, or non-infectious causes such as contact dermatitis or psoriasis. The inflammation may be caused by irritants in the environment. Common causative organisms include candida, chlamydia, and gonorrhea. The cause must be properly diagnosed before a treatment can be prescribed. A common risk factor is diabetes.

Posthitis can lead to phimosis, the tightening of the foreskin which makes it difficult to retract over the glans. Posthitis can also lead to superficial ulcerations and diseases of the inguinal lymph nodes.