Hydrochlorothiazide (HCTZ) is a drug with diuretic action, which its use is mainly associated with the treatment of arterial hypertension and it can also be used in other types of treatment, such as congestive heart failure, liver cirrhosis and others. HCTZ is banned by the World Anti-Doping Agency (WADA)¹. This because, in recent years, this drug has been used by athletes in sports competitions of different modalities for the purpose of weight-loss and/or to disguise the use of other prohibited substances by WADA. Due to this the quality-control of this drugs in pharmaceutical formulation is very important, as well as in urine sample is interest to WADA. The Several analytical methods have been used for drugs detection in quality control and anti-doping analysis, but most notably chromatographic methods with UV and mass spectrometry detection. Nevertheless, electroanalytical methods can offer easy on-site screening method of samples, providing a portable, simple and low-cost electrochemical sensors. In this context, we present the HCTZ determination using an unmodified electrode of boron-doped diamond (BDD) as electrochemical sensor. The BBD electrode was used with square wave voltammetry (SWV) technique was used for a fast and sensitive detection of HCTZ in urine and its possible application as a screening method in the doping control. The measurements were carried out in an electrochemical cell with three electrodes, using BDD as the working electrode (with doping of 8.000 ppm and an area of 0.13 cm²) and Ag/AgCl (saturated KCl) and platinum wires as reference and auxiliary electrodes, respectively. The BDD electrode was pretreated cathodically and anodically in 0.5 mol L−1 H2SO4: for the cathodic pretreatment, first was applied a positive current of +0.001 A for 120 s and then applied −0.03 A for 360 s; for the anodic pretreatment was applied the same currents above, but first was applied the negative current. The two pretreatments of BDD electrode were evaluated and the cathodic treatment was chosen, which was performed before each analysis. The HCTZ electrochemical behavior was studied by cyclic voltammetry (CV) in Britton-Robson buffer (BRB) solutions (pH 2 to 12) and other electrolytes. The best conditions in function to higher sensitivity and a better selectivity for HCTZ detection were obtained in 0.1 mol L^-¹ BRB pH 2.0 at BDD electrode, where an oxidation process for HCTZ at +1.3V was observed. The repeatability of SWV and differential pulse voltammetry (DPV) techniques were evaluated for a reproducibible and sensitive detection of HCTZ. The relative standard deviations of 2.6% and 6.5% were obtained for 10 determination of 1 mmol L-1 HCTZ by SWV and DPV, respectively. Thereby, SWV technique was chosen to determinate of this analyte with all parameters previous optimized: potential step of 5 mV, amplitude of 80 mV and frequency of 40 Hz. Linear range for HCTZ quantification was obtained from 0.8 to 6.9 μmol L^-1 (r²=0.999) with low LOD of 0.2 μmol L^-1. The addition-recovery studies in pharmaceutical samples containing HCTZ were obtained around 100 %. The interference study in urine samples are being performed. Therefore, proposed method offers a fast and simple alternative for the quality control of HCTZ. Furthermore, due to good sensitive achieved using the BDD electrode with SWV detection, this sensor presents a perspective to be a screening method for doping control analysis of HCTZ in urine samples.