Among our 20 families with LGMD2, 10 were documented to have muscle-specific calcium-activated neutral protease 3 (calpain-3) deficiency. Consanguinity was present in all. The current ages of the index cases were between 12 and 23 years, and there were additional nine members affected. Clinically, the patients showed mild courses; none of the cases below age 30 lost autonomy so far. The dystrophy is mainly proximal and atrophic with calf enlargement and scapular wasting in some. In three cases walking was delayed. Creatine kinase levels were at least 10 times elevated. All obligate carriers had normal creatine kinase levels. Five families shared the same 551 delA frameshift mutation. In four of these families there was the same core haplotype, whereas one was distinct suggesting an independent origin. Calpain-3 deficiency in general is a mild muscular dystrophy during childhood.