Benign is any condition which, untreated or with symptomatic therapy, will not become life-threatening. It is used in particular in relation to tumors, which may be benign or malignant. Benign tumors do not invade surrounding tissues and do not metastasize to other parts of the body. The word is slightly imprecise, as some benign tumors can, due to mass effect, cause life-threatening complications. The term therefore applies mainly to their biological behaviour.

Tumors may be benign but at risk for degeneration into malignancy. These are termed "premalignant".