Malignant hyperthermia (MH) is rarely associated with specific myopathies or musculoskeletal abnormalities. Three clinical investigations of MH associated with either non-specific myopathies or congenital disorders in three separate families are presented. Two of these cases also show evidence of exercise-induced rhabdomyolysis. In each case MH susceptibility was confirmed by in vitro contracture testing of quadriceps muscle. DNA sequence analysis of each kindred revealed the presence of a common novel mutation that results in an arginine401-cysteine substitution in the skeletal muscle ryanodine receptor gene (RYRI). Haplotype analysis using chromosome 19q markers indicated that the three families are likely to be unrelated, providing confirmation that the MH/central core disease region I of RYRI is a mutation hot spot.