We present a microelectromechanical systems (MEMS) tunable metamaterial, Fabry-Perot interferometer with a widely tunable mid-infrared response. An array of subwavelength holes in a gold film is suspended above a gold reflector, forming an interferometer cavity whose length can be modulated over a range of 1.7 to 21.67 mu m using MEMS electrostatic actuation. Reflectance spectra exhibit the convolution of extraordinary optical transmission through the holes and Fabry-Perot resonances with free spectral ranges from 2900 to 230.7 cm(-1). Measuring the free spectral range enables us to perform in situ interferometric calibration of the cavity length. We present a simple analytical model that describes the experimental and simulated results. This device shows promise as a surface-enhanced sensing substrate with a tunable spectral response.