An ultraviolet (UV)-based advanced oxidation process (AOP), with hydrogen peroxide and medium-pressure (MP) UV light (H(2)O(2)/UV), was used as a pretreatment strategy for biofilm control in water. Suspended Pseudomonas aeruginosa cells were exposed to UV-based AOP treatment, and the adherent biofilm formed by the surviving cells was monitored. Control experiments using H(2)O(2) or MP UV irradiation alone could inhibit biofilm formation for only short periods of time (<24 h) post-treatment. In a H(2)O(2)/filtered-UV (>295 nm) system, an additive effect on biofilm control was shown vs filtered-UV irradiation alone, probably due to activity of the added hydroxyl radical (OH•). In a H(2)O(2)/full-UV (ie full UV spectrum, not filtered) system, this result was not obtained, possibly due to the germicidal UV photons overwhelming the AOP system. Generally, however, H(2)O(2)/UV prevented biofilm formation for longer periods (days) only when maintained with residual H(2)O(2). The ratio of surviving bacterial concentration post-treatment to residual H(2)O(2) concentration played an important role in biofilm prevention and bacterial regrowth. H(2)O(2) treatments alone resulted in poorer biofilm control compared to UV-based AOP treatments maintained with similar levels of residual H(2)O(2), indicating a possible advantage of AOP.