Batch adsorption experiments were carried out in order to evaluate the maximum adsorption conditions of pharmaceutical trimetoprim from real wastewater on pillared clay using a full factorial design. The five factors were temperature, the initial pH of the solution, initial concentration, agitation and dosage of adsorbent. The optimization of the factors to obtain maximum adsorption was carried out by incorporating effect plots, normal probability plots, interaction plots, analysis of variance (ANOVA), Pareto charts, surface plots, and contour plots. The statistical design experiments, designed to reduce the total number of experiments required, indicated that, within the selected conditions, all the parameters influenced at a significance level of 5%. In addition, some of the possible interactions between these parameters also influenced the adsorption process, especially those that were of first order. A regression model was suggested and fitted the experimental data very well.