This study demonstrates the feasibility of using fibre Bragg grating (FBG) sensors to monitor the effects of hygrothermal ageing on the axial strains in a cylindrical epoxy specimen with a centrally located optical glass fibre. A 24 mm long FBG, inscribed on the fibre, is used to monitor the moisture absorption in the epoxy, immersed in distilled water at 50 degrees C for 2330 h. Hygromechanical simulations support the experimental strain data when the first part of the absorption process is neglected or when a variable coefficient of moisture expansion is used. Also, the effects of using average moisture or when it is distributed according to Fick's law are negligible. The FBG response also indicates the appearance of progressive debonding after sufficient exposure to moisture. (C) 2008 Elsevier Ltd. All rights reserved.