Human gait patterns differ considerably between the sexes. Therefore sex specific trunk muscle activation patterns can be expected. Healthy volunteers of both sexes (51 women, 55 men) walked on a treadmill at speeds from 2 to 6 km/h. Surface electormyography was recorded from five pairs of trunk muscles. Grand averaged root mean square (rms) curves and amplitude normalised curves were calculated. Mean amplitudes and relative amplitudes were calculated as well. Mean amplitudes as well as relative amplitude levels were not generally sex specific, but differed for single muscles. Grand averaged rms curves of all investigated muscles differed between sexes. At low walking speeds, differences mostly originated from mean amplitude level differences, alternating between sexes. At higher walking speeds, amplitude curves became more phasic, differences again alternated between sexes. Therefore, trunk muscle co-ordination during gait is sex-specific. Any interpretation of trunk muscle co-ordination patterns during gait requires sex specific normatives.