Excessive accumulation of intracellular calcium in Duchenne muscular dystrophy (DMD) may be a necessary step in the process that causes muscle damage in this disease. Because of this possibility, a controlled trial of the calcium channel blocking agent nifedipine was undertaken. One hundred and five patients were randomized and treated in a double‐blind manner for 18 months. Muscle strength, contractures, functional ability, cardiopulmonary changes, and laboratory data were monitored. The dose of nifedipine was 0.75‐1 mg/kg/day in the first 6 months and 1.5‐2 mg/kg/day for the next 12 months. Satisfactory blood levels of nifedipine were attained. The study had a power greter than 0.99 to detect a slowing of the illness to 25% of its original rate of progression. No significant improvement was demonstrated in the treated group. One or more of the frequent mild side effects of flushing, dizziness, and leg edema, often associated with the use of nifedipine in adults, occurred transiently in approximately one‐half of the patients in the nifedipine group and in 21% of the placebo group. Four patients died, two on nifedipine and two on placebo. This study demonstrates that nifedipine is safe to administer in children, but that it is without beneficial effect on the course of DMD.