Mucopolysaccharidoses (MPS) are a group of lysosomal storage disorders, characterized by the deficiency/absence of one of the enzymes involved in the intralysosomal degradation of glycosaminoglycans (GAGs). The quantitative determination of urinary GAGs using dimethylmethylene blue (DMB) shows high reliability. However, the logistics and staff for this method are not always available in primary care centers. Sending urine samples to reference laboratories increases the cost and delays the diagnosis. Thus, the aim of this article is to develop and evaluate a simple and low-cost visual test (GAG-test s ) for the screening of urine samples from patients under suspicion of suffering from MPS. The purpose is to narrow down the number of samples to be assayed through the quantitative method. A measure of 50 ml urine was added to 2 ml DMB solution. A color change from dark blue to purple indicates an excess of GAGs. The quantitative analyses showed a significant difference between controls' and patients' concentrations (Po0.05). After optimization of the composition, positive and negative results obtained with the qualitative test were able to discriminate between normal urines and those from patients suffering from mucopolysaccharidosis. Therefore, GAGtest s has proved to be a useful tool for the prior diagnosis of patients suffering from mucopolysaccharidosis, reducing the number of individuals with whom investigations should be continued.