Proteus mirabilis cause urinary tract infections which are recurrent and can lead to formation of urinary calculi. Both bacterial and the host factors are involved in the development of urolithiasis. To determine the impact of glycosaminoglycans (GAGs) in the formation of P. mirabilis-induced urinary stones, we investigated the in vitro crystallization, aggregation and adhesion of crystals in the presence of GAGs naturally appearing in urine. Crystallization experiments were performed in synthetic urine infected with P. mirabilis in the presence of: hyaluronic acid (HA), heparan sulfate (HS), chondroitin sulfate A, B and C (ChSA, ChSB, ChSC). The intensity of crystallization and aggregation were established by counting particles and phase-contrast microscopy. To analyze the adhesion of crystals, we used normal urothelium and 45Ca isotope-labeled crystals. In the presence of ChSC, both the size of the crystals formed and their number were higher compared with the control. GAGs increased crystals adhesion to the cells, but only for ChSA this effect was significant. Chondroitin sulfates, which accelerate the first stages of infection-induced stones formation, may play an important role in the pathogenesis of infectious urolithiasis.