Selective inhibitors of inducible nitric oxide synthase (iNOS) have therapeutic potential for diseases mediated by overproduction of nitric oxide (NO). Previously reported arginine-based NOS inhibitors lack iNOS selectivity, while N-(Iminoethyl)-L-lysine (NIL) is a selective iNOS inhibitor with 30-fold selectivity over endothelial NOS (eNOS). We replaced the carboxyl group of NIL with a vicinal glycol to yield N-(5(S)-amino-6,7-dihydroxyheptyl)ethanimidamide dihydrochloride (2). Compound 2 inhibits iNOS with an IC50 of 12 µM (slightly less potent than NIL) but shows a striking ~700-fold selectivity for iNOS over eNOS and 12-fold selectivity over neuronal NOS (nNOS). Chirality is critical for activity, as 2 is ~4 times more potent than its diastereomer 11. We have identified 2 as a highly selective iNOS inhibitor and shown that the vicinal diol moiety is an effective isostere for the carboxyl group of NIL.