Research concerning the long-term behaviour of fibre reinforced polymer (FRP) composites in civil engineering applications is increasing, as key actors in this industry recognize the existence of many knowledge "gaps" that still need to be fulfilled. Several competing mechanisms may affect the durability of FRPs during exposure to hygrothermal ageing conditions, and in the specific case of pultruded glass-fibre reinforced polymer (GFRP) profiles, comprehensive and validated data on their durability is still limited. The typically long service lives required for most structures together with the low frequency of routine inspection and maintenance operations in civil infrastructure enhance the importance of having reliable durability data and suitable prediction models for the long-term performance of these materials. This study presents results of an experimental and analytical study designed to investigate the effects of hygrothermal ageing on the durability and long-term performance of two commercial GFRP profiles made of two alternative resin systems - unsaturated polyester (UP) and vinylester (VE), both comprising the same fibre content and architecture. Test specimens of the two types of profiles were subjected to different ageing environments, namely immersion in demineralised and salt water at three different temperatures (20 degrees C, 40 degrees C, and 60 degrees C) and continuous condensation at 40 degrees C for up to two years, and were tested after a desorption period, thus including the potential property recovery after drying to constant mass due to the reversible nature of some of the physical degradation mechanisms. The performance of both profiles was analysed and compared regarding their mechanical response in tension and flexure after being subjected to hygrothermal ageing. The experimental data thus gathered were subsequently used to derive analytical models for the prediction of long-term effects and service life of pultruded GFRP profiles based on the Arrhenius law. This provided estimates for the retention of strength and moduli in tension and flexure, for both UP and VE pultruded GFRP profiles when exposed to different hygrothermal environments.