Mild self-etching adhesive systems modify and/or incorporate the smear layer into the resin-infiltrated demineralised dentin. Some factors such as type of bur and use of water spray might affect the thickness of the smear layer on substrates, enamel and dentin. Because of this, the present study evaluated the thickness of smear layers created by different finishing procedures, after the application of three simplified self-etching primers (Adper Prompt L-Pop and two experimental formulations) on enamel and dentin. After the application and removal of the primers' resinous component, the specimens were prepared for examination under a scanning electron microscope. Smear layers were thicker on enamel than on dentin, irrespective of the finishing methods used. Therefore, different thicknesses of smear layer on enamel/dentin might be an important factor to consider when evaluating the bonding efficacy of self-etching adhesives to both tooth substrates.