Hashimoto's thyroiditis is the most frequent cause of hypothyroidism. In the regions with no iodine deficiency, it is more frequent in women and oftentimes has a familial association. The symptoms and signs of hypothyroidism are systemic and depend on the duration and intensity of the thyroid hormone deficiency. Neuromuscular manifestations are seldom the only symptoms and signs present. We present the case of a young patient with severe myopathy, where rhabdomyolysis was the sole manifestation of severe hypothyroidism secondary to Hashimoto's thyroiditis.