A noninvasive blood glucose monitoring system is presented. A microwave microstrip patch resonator antenna is used to measure the displacements on its resonant frequency while being on the individual’s tongue. These changes are due to inversely proportional changes on the relative permittivity of the tongue, which are directly related with changes on the user’s blood glucose level. Simulations are performed to assess the feasibility of the configuration of the system and the veracity of the principles adopted and the hypothesis proposed. Then, highly detailed explanations of physical implementation and evaluation with diabetic and non-diabetic volunteers and comparison with commercial invasive glucometers are shown, and final results are discussed.