The family of two-pore domain potassium (K_2P) channels is critically involved in central cellular functions such as ion homeostasis, cell development, and excitability. K_2P channels are widely expressed in different human cell types and organs. It is therefore not surprising that aberrant expression and function of K_2P channels are related to a spectrum of human diseases, including cancer, autoimmune, CNS, cardiovascular, and urinary tract disorders. Despite homologies in structure, expression, and stimulus, the functional diversity of K_2P channels leads to heterogeneous influences on human diseases. The role of individual K_2P channels in different disorders depends on expression patterns and modulation in cellular functions. However, an imbalance of potassium homeostasis and action potentials contributes to most disease pathologies. In this review, we provide an overview of current knowledge on the role of K_2P channels in human diseases. We look at altered channel expression and function, the potential underlying molecular mechanisms, and prospective research directions in the field of K_2P channels.