ABSTRACT Introduction: ACT DMD was a 48‐week trial of ataluren for nonsense mutation Duchenne muscular dystrophy (nmDMD). Patients received corticosteroids for ≥6 months at entry and stable regimens throughout study. This post hoc analysis compares efficacy and safety for deflazacort and prednisone/prednisolone in the placebo arm. Methods: Patients received deflazacort (n = 53) or prednisone/prednisolone (n = 61). Endpoints included change from baseline in 6‐minute walk distance (6MWD), timed function tests, estimated age at loss of ambulation (extrapolated from 6MWD). Results: Mean changes in 6MWD were ‐39.0 m (deflazacort; 95% confidence limit CL, ‐68.85, ‐9.17) and ‐70.6 m (prednisone/prednisolone; 95% CL, ‐97.16, ‐44.02). Mean changes in 4‐stair climb were 3.79 s (deflazacort; 95% CL, 1.54, 6.03) and 6.67 s (prednisone/prednisolone; 95% CL, 4.69, 8.64). Conclusions: This analysis, limited by its post hoc nature, suggests greater preservation of 6MWD and 4‐stair climb with deflazacort vs. prednisone/prednisolone. A head‐to‐head comparison will better define these differences. Muscle Nerve 58: 639–645, 2018