Thirty-nine members, ages 1 to 67 years, of a Swedish family with rippling muscle disease (RMD) were investigated to assess genotype-phenotype correlations. Clinical, neurophysiological, and muscle morphological examinations were performed. Genetic analysis was performed in 38 individuals. Twenty-three patients had percussion-induced muscle mounding (PIMM) and percussion-induced rapid contractions (PIRC). Rippling and hyperCKemia were not found in all patients. Weakness was minor or absent. The electromyogram showed absence of electrical activity in ripples and PIMM, and muscle biopsy specimens confirmed caveolin-3 deficiency and absence of caveolae. Genetic analysis revealed a CAV3 c.G136A transition resulting in a p.A46T missense mutation in affected family members. The phenotype in these 23 cases of RMD with this mutation appears to be homogenous, benign, and nonprogressive. The presence of PIMM and PIRC seems to be diagnostic at all ages, whereas the absence of hyperCKemia and rippling does not exclude the diagnosis.