The fabrication and characterization of quantum cascade (QC) disk lasers at 5 μm wavelength is reported. The QC scheme yields several advantages for the disk geometry: an inherently transverse magnetic polarization, tailorable wavelength, and unipolar carrier transport. The low loss whispering gallery resonator allows small devices, 17–125 μm in diameter, and low threshold currents (2.85 mA for a 17 μm diameter disk) with a size independent pulsed threshold current density of 1.2 kAcm−2 at 15 K. From the threshold current density the quality factor of the disks is estimated at Q∼3500. The emission spectra show single and multiple whispering gallery modes.