Gerontius (; Latinized Greek for 'old man') can refer to:
Music and literature The Dream of Gerontius, a 1900 choral work by Edward Elgar, a setting of a poem of the same name by John Henry Newman The Dream of Gerontius, the poem by John Henry Newman
People Gerontius (bishop of Milan), bishop of Milan (462-465) Gerontius of Cervia, 6th-century Italian bishop Gerontius, Metropolitan of Moscow, 1473-1489 Gerontius (magister militum), early 5th-century Roman general Gerontius (commander), early 4th-century Roman commander of Tomis
Fiction Gerontius, a 1989 novel by James Hamilton-Paterson Gerontius, the given name of the Old Took, a hobbit mentioned in J. R. R. Tolkien's fantasy series The Lord of the Rings
See also Geraint (given name) (the Welsh form of Gerontius)