Aims Stressful environmental conditions influence both bacterial growth and expression of virulence factors. In the present study, we evaluated the influence of NaCl on Aeromonas hydrophila adhesiveness at two temperatures. This agent is often involved in clinical cases; however, its pathogenic potential is still not fully understood. Methods and Results Bacteria were grown in presence of 1.7%, 3.4%, 6.0% NaCl over a 188 day period and then reinoculated in fresh Nutrient Broth with incubation at 4 and 24 degrees C. Bacterial adhesiveness was tested on Hep-2 cells, and specimens were processed for light, scanning and transmission electron microscopy. Adhesive capacity decreased over time with an increase in reduction percentages depending on NaCl concentrations. At 1.7% NaCl, the reduction was apparently temporary and adhesiveness rapidly recovered in revitalized bacteria, while 3.4%, 6.0% NaCl seemed to be detrimental. Normal, elongated and filamentous bacteria retained adhesiveness capability, although with reduced expression, while in spherical cells, this property seemed to be lost or dramatically reduced. Conclusions Our study shows that high osmolarity plays a significant role in adhesion inhibition, therefore having possible implications in the pathogenesis of the infections by Aer. hydrophila. Significance and Impact of the Study This study intends to give a contribution to a better understanding of the pathogenic role of this bacterium whose pathogenicity is still under debate.