The onset of Rayleigh-Benard convection in a liquid 3He-4He mixture (3He concentration = 2.22%) rotating about a vertical axis has been investigated at temperatures between 20.5mK and 92.5mK above the superfluid transition temperature. Rotation is found to stabilise the fluid against the onset of convection in accordance with the conclusion of a linear stability analysis. Except for small angular velocities the critical Rayleigh number for the onset of convection is lower than that predicted by a linear stability analysis. We attribute this behaviour to the production of an azimuthally periodic mode of convection confined to the sidewall of the cell. A second convective onset is observed when the angular velocity excees a critical value which is dependent upon the temperature. We believe this corresponds to the onset of full body convection. Hysteretic effects are evident.