This essay discusses the many aspects of sin and concupiscence in Augustine’s Confessions. It first analyses how these concepts function in the narrative about his early years, and then explores the story of Augustine’s early and later adolescence. From several references in Books 3 and 4, it is concluded that Augustine had strong—albeit temporary—homo-erotic feelings. The following books evidence his lasting longing for concubitus with a woman, first experienced with his ‘Una’ and later with an interim concubine.This sinful concupiscential desire (several times referred to as his ‘disease’) even beset the monk and bishop Augustine at the time he wrote his literary masterpiece: in Book 10 he confesses nocturnal emissions caused by his sex dreams. Although particularly in the later parts of Book 10 (esp. 10,41ff.) Augustine describes concupiscentia as having a rather broad spectrum of meanings, its sinful sexual meaning prevails in the whole of his Confessions. The same appears to go for a related concept such as libido. All this leads to the conclusion that confessio in the sense of confession of sexual sins is an essential feature of the title and contents of Augustine’s work.