Absolute quantum yields for primary H atom formation (Φ_H) were measured under collision-free conditions for the room-temperature gas-phase dissociation of acetylene (C₂H₂) after photoexcitation at 193.3 nm and at the H-atom Lyman-α wavelength (121.6 nm) by a pulsed laser photolysis (LP)-laser-induced fluorescence (LIF) 'pump-and-probe' technique. Using HCl and CH₄ photolysis at 193.3 and 121.6 nm, respectively, as a reference, values of Φ_H (193.3 nm)=0.94± 0.12 and Φ_H (121.6 nm)=1.04± 0.16 were obtained which demonstrate that for both photolysis wavelengths the H+C₂H product channel dominates the primary C₂H₂ photochemistry.