Hypokalemic periodic paralysis (HPP) is a rare hereditary or acquired condition resulting in episodes of severe muscle weakness, usually in the setting of strenuous exercise with a high carbohydrate diet. The most common form of HPP is inherited (familial hypokalemic periodic paralysis) and is caused by either a mutation in the skeletal muscle calcium channel gene CACNA1S (HPP type 1) or the skeletal muscle sodium channel gene SCN4A (HPP type 2). Thyrotoxicosis can also cause HPP (acquired HPP). Familial HPP follows an autosomal dominant inheritance pattern and exhibits incomplete penetrance, with a male predominance. Though ~80% of cases of familial HPP are caused by CACNA1S, SCN4A, or KCNJ2 gene mutations, the genetic cause of the rest remains undetermined.