This paper describes an efficient CE-UV-ESI-TOF/MS method for the determination and quantitation of intact insulin (INS) in a pharmaceutical formulation. The CE conditions were optimized to avoid the adsorption of proteins onto the capillary wall. Particular attention was paid regarding the choice of the internal standard (IS). A strategy based on multiple injections was selected and the methodology was validated according to international guidelines. The optimized method was applied with success to the analysis of INS formulations obtained from regular and parallel markets.