The present Raman investigation of anhydrous alloxan and the misnamed alloxan monohydrate suggests that some of the assignments previously made on basis of the IR spectrum of the anhydrous compound must be changed, i.e., the ones related to the NH stretching and ring breathing modes. The hydrogen bonding network in the crystal of the so called alloxan monohydrate, although extensive, is not strong enough to cause substantial frequency shifts in the NH and CO stretching modes.