The attachment of diatoms to surfaces is an important and poorly understood step in the development of biofouling communities. Experiments were performed in vitro on a common fouling diatom (Achnanthes longipes) to determine the influence of the base material and bacterial conditioning on diatom attachment. The first series of experiments compared attachment of A. longipes to four different base materials, and the influence of a bacterial film on attachment to these materials. A. longipes preferentially attached to polystyrene, a hydrophobic surface, but was inhibited by the presence of a bacterial biofilm. On other surfaces, bacteria either facilitated or had no effect on algal attachment. The second series of experiments found no difference in the attachment of A. longipes to a surface covered with bacterial exopolymer compared to a surface with a film of living bacteria. Attachment of A. longipes was found to vary depending on the conditions under which the bacterial film developed and the species of bacteria within the film. These results help to illustrate the complexity of the relationship between surfaces and attaching organisms and show that bacteria may either facilitate, have no effect or inhibit attachment by diatoms. The mechanisms underlying these patterns require further investigation.