Corrosion resistance of stainless steels depends on metallurgical and production variables. Corrosion is highly unwanted in stainless steels because of their purpose, to have high corrosion resistance and high mechanical properties. In this paper, one example of corrosion occurrence in X5CrNi18-10 stainless steel will be analyzed. Samples were taken from two different cold deformed sheets that had porosity on similar places. Chemical analysis and metallography were done in laboratory in order to determine the reason for corrosion occurrence.