In this study, the determination of indigo carmine (IC) dye in environmental water samples by square-wave voltammetry (SWV) using a cathodically pretreated boron-doped diamond (BDD) electrode is proposed. This dye showed an irreversible oxidation process onto BDD electrode with predominant hydrogen (cathodic pretreatment) or oxygen (anodic pretreatment) terminations. Comparatively, the cathodically pretreated BDD electrode provided a better performance for the anodic response of IC and, therefore, it was selected as working electrode to perform the voltammetric determinations. The electrochemical behavior of IC dye was investigated on the BDD electrode, and the electrochemical features of this molecule were determined, as the number of electrons transferred, apparent diffusion coefficient (Dapp) and adsorption. The neglectful adsorption of IC molecule on the BDD surface comparatively to a glassy carbon electrode surface was evidenced. Using SWV under the optimized experimental conditions, IC was determined in the linear concentration range from 0.5 to 84.1 pmol L-1, with a limit of detection of 0.058 pmol L-1. By applying assays of standard addition, IC was successfully quantified in water samples, with excellent results of recovery percentage. (C) 2016 Elsevier B.V. All rights reserved.