This study evaluated the feasibility of measuring steady-state oxygen uptake (VO2) during the 6-min walk test (6MWT) in adults with cerebral palsy (CP) who walk without support and whether there is construct validity for net 6MWT VO2 as a measure of their walking ability. Cardiorespiratory variables were assessed at rest and during the 6MWT in 15, independently ambulatory adults, 21-41 years old, with CP. The Gross Motor Function Measure dimensions D and E (GMFM-D and GMFM-E) quantified walking-related skills. Steady-state VO2 was achieved during the 6MWT. After controlling for body mass and speed, the net 6MWT VO2 was strongly related to GMFM-D (r=-0.58, ρ=0.03) and GMFM-E scores (r=-0.66, ρ=0.007). We conclude that for young adults with CP who walk without support, it is feasible to measure steady-state VO2 during the 6MWT and that the net 6MWT VO2 has construct validity as a measure of walking ability.