Display omitted This work describes the development of a disposable and wearable screen-printed electrochemical sensor for the determination of chloride ions. The sensor includes three screen-printed electrodes: a working, an auxiliary (both carbon paste electrodes), and an Ag/AgCl pseudo-reference electrode. The sensor works by measuring the Nernstian shift of the voltammetric peak potential of ferrocenemethanol in the presence of chloride ions, due to the use of a pseudo-reference electrode in the electrodic system. The measurements are easily taken by dropping the sample onto the electrodic surface. Different flexible materials, including textiles, were studied as substrates of the electrodic system. A study of ink adherence and conductivity in these materials was carried out. The use of Gore-Tex® displayed good ink adherence, acceptable conductivity and waterproof properties. These features make it an excellent support for wearable sensors. The reproducibility and repeatability, in terms of relative standard deviation values of the developed Gore-Tex sensor, were below 3% (n=5) and the detection limit was 0.2mM (α=β=0.05). The sensor was successfully applied to determine the chloride content in sea water.