The men's 800 metres event at the 1991 IAAF World Indoor Championships was held on 8, 9 and 10 March.
First 2 of each heat (Q) and next 2 fastest (q) qualified for the semifinals.
[1] First 3 of each semifinal (Q) qualified directly for the final.
[2] [3] Note: William Tanui had originally won in 1:46.94, but was later disqualified for breaking from his lane too early.