Uniform oscillations of supercontinua, generatedwith microstructured fibre, have been observed and investigated.The oscillations are uniform in the sense that the opticalpower through the fibre changes with a regular and periodicwaveform and the spectral bandwidth of the transmitted lightchanges correspondingly. The oscillations are continuous overperiods of hours and the spectral width ranges from the octavespanningcondition (∼ 310-THz wide at 20 dB below the maximum)to zero broadening of the input light. The correspondingcontrast ratio of the fluctuating output light signal is as highas 0.75. Silica photonic crystal fibre with hexagonal air-holestructure and core diameter of 2.0 μm was used for the supercontinuumgeneration. The oscillations are produced when atleast 15mm of fibre is allowed to extend from the mount ofthe fibre launcher. Arguments in terms of thermal behaviour areused in an attempt to explain the fluctuations of light throughthe microstructured fibre. This appears to be the first occasionin which such behaviour has been reported.