Long-term follow-up studies in Charcot-Marie-Tooth disease type 1 duplication (CMT1A) are scanty. Here we describe a longitudinal study in a CMT1A pedigree. Our CMT1A pedigree comprised 11 examined patients, ages between 13 and 83 (median, 36) years, serially evaluated for up to 26 years. In all 11 patients we carried out electrophysiological evaluation, and in three of them magnetic resonance imaging (MRI) of lower-limb musculature. The 54-year-old proband patient, yearly examined as of age 28, developed at age 48 gradual and progressive distal lower-leg weakness ascending to thigh musculature. His serial electrophysiological studies showed diffuse slowing of motor conduction velocity, absence or severe attenuation of distal compound muscle action potentials, and spontaneous muscle activity in the tibialis anterior and rectus femoris. Two MRI studies of lower limbs, at ages 51 and 54, showed extensive fatty atrophy of lower-leg musculature, and progressive and distally accentuated fatty atrophy of anterior and posterior femoral muscles. An outstanding finding in the first MRI was the presence of marked edema of anterior femoral musculature, which to a great degree was replaced by fatty atrophy in the second study. Muscle edema was also noted in lower-leg and posterior femoral musculature. There was minimal fatty atrophy of the gluteus maximus, the remaining pelvic muscles being preserved. The other ten patients showed mild or moderate phenotype, which remained quiescent over the period of observation. Electrophysiological studies disclosed diffuse and uniform slowing of nerve conduction velocities; in no case was spontaneous muscle activity recorded. MRI showed the CMT1A characteristic pattern of distally accentuated fatty atrophy involving foot and lower-leg musculature with preservation of thigh musculature. We conclude that a small proportion of patients with CMT1A develop a late progression of disease manifested with accentuated distal leg weakness ascending to involve thigh musculature, and that long-term follow-up is essential for its detection.