This study evaluated the effects of additional and extended acid etching on microtensile bond strength (muTBS) of two adhesive systems to sound (SD) and caries-affected dentine (CAD). Flat surfaces of CAD surrounded by SD of 36 extracted carious third molars were assigned to four treatments (i): self-etching adhesive system (Clearfil SE Bond) applied to dentine surfaces following manufacturer's instructions (MI); (ii) after additional etching for 15 s (35% phosphoric acid, PA); (iii) total-etch one-bottle adhesive (Single Bond) applied to dentine surfaces following MI; or (iv), after etching for 45 s with PA. Composite 'blocks' were built on bonded surfaces and restored teeth were vertically sectioned to obtain bonded slices of 0.7 mm thick. Slices were trimmed to create hourglass-shaped specimens (cross-sectional area of 1 mm(2)), which were tested under tension in a universal testing machine. Additional CAD and SD samples were prepared for scanning electron microscopy observations. Additional and extended etching significantly increased muTBS to CAD; however, muTBS of both adhesives to CAD were significantly lower than to SD. Additional and extended etching can improve bonding to CAD; however, adhesives applied on SD showed the best results for bonding.1125458464