In this article, the authors report how thin (10 nm or less) oxide-free phosphorus containing films can be formed on chromium and stainless steel on treatment with an organophosphorus acid (etidronic acid) using an anaerobic cell and a “bench” treatment. Core level and valence band x-ray photoelectron spectroscopy were used to study the films formed. Compositional variations were interpreted through the use of band structure and X-alpha calculations. The chromium study indicates that the etidronate at least partially decomposed to form phosphate. Some phosphide was observed for the bench treatment. Polished 316 L chromium containing stainless steel treated in 3M etidronic acid formed a thin phosphate containing film when using the bench treatment, but a film characteristic of etidronate when the anaerobic cell was used. Film changes during air exposure and exposure to 1M sodium chloride solution showed decomposition, the most resistant film being that of the etidronate on stainless steel. This thin etidronate film result shows that oxide-free etidronate films can be formed on stainless steel and these films have corrosion inhibition properties, which may find application in implant fabrication.