The reading of Genesis 18,20 does not make clear what the sin of Sodom is.The Hebrew text only says that the transgression of the inhabitants of that city was greatly aggravated: “ְוחַטָּאתָּם ” – “vëchatåtåm” - “כָּבְדָּה ” – “khåvëdåh” - “מְאֹד ” – “mëod”. Even the passage in Gen 19,5 gives no clue to a specific sin: in this passage it seems more evident that the sodomites are violating the normal canons of hospitality. But then why do popular imaginations and some interpreters identify the sin of Sodom with homosexuality? This research will demonstrate that a number of factors led to this type of interpretation. First it was understood that Gen 19,5 gave an indication of the sexual orientation of the inhabitants of Sodom; then the passages of Leviticus 18,22 and 20,13 were invoked to regulate this opinion; the next step was to connect Gen 18,20 and 19,5 with Paul’s comments in Romans 1 in which the sin of Sodom was associated with homosexual sex. This connection was sustained by Augustine and also by the author of “Visio Sancti Pauli”. The coming together of these factors was the catalyst for later traditions in which the sin of Sodom is presented as homosexual sex.