The morphology and chemistry of the failure of adhesively bonded phosphoric acid anodising (PAA)-treated aluminium alloy (2014A) has been investigated by XPS and transmission electron microscopy/parallel electron energy-loss spectroscopy (TEM/PEELS). Cyclic fatigue tests were undertaken using tapered double cantilever beam joints in water. Specimens were prepared for analysis from the crack-tip region and from areas ahead and behind the crack-tip (i.e. the unfractured and the fatigue-fractured and water-exposed regions). A failure at the crack-tip is shown by both XPS and energy-filtered TEM (EFTEM) to be very close to the oxide/adhesive interface, but in the adhesive phase. Behind the crack-tip, a failure surface devoid of adhesive residues, oxide hydration is observed. An observation made at regions well behind (10–15 mm) the crack-tip indicates that mechanical damage of the hydrated layer occurs as a result of the cyclic-fatigue displacement. These results indicate that hydration is a post-failure event for the system under study in this work.