Acinetobacter baumannii, an important nosocomial pathogen is usually found on various surfaces in the hospital environment. In this work, the ability to form biofilms on the surface of sterile coverslips by one clinical isolate of A. baumannii was studied. Sessile cells which adhered to coverslips after being immersed in a nutrient-deficient mineral medium were observed by epifluorescence and scanning electron microscopy at various times of incubation. A rapid increase in the number of sessile cells in young biofilms, followed by a slower increase of such cells was found. At 48 h biofilms were clearly visible and an amorphous material similar to the exopolysaccharide described in some other bacteria covered sessile cells was evident. Biofilm formation by A. baumannii probably favours its maintenance on solid surfaces in the hospital environment and protects the micro-organism against some antibacterial factors.