In this paper, we evaluate the performance of a dual-hop fixed-gain amplify-and-forward (AF) relay system in the presence of co-channel interference (CCI) at the destination node. The desired user channels are assumed to follow the Rayleigh distribution and different fading environments for interferers' channels have been considered, Rayleigh, Nakagami-m, and Rician. We derive exact closed-form expressions for the outage probability and the symbol error rate (SER) for the Rayleigh and Nakagami-m cases, and accurate approximations for the case of Rician distributed interferers' channels. Both, the independent non-identically distributed (i.n.d.) and independent identically distributed (i.i.d.) cases of interferers' channels have been considered in this paper. Furthermore, a look into the asymptotical high signal-to-noise ratio (SNR) performance has been taken and the diversity order and coding gain of the proposed fading environments are compared. Finally, the Monte Carlo simulations are provided to validate the analytical and asymptotic results and to illustrate the effect of interference on the system performance.