We investigate the outage probability and the average bit error rate (BER) of a dual-hop fixed gain relaying system in the presence of co-channel interference and thermal noise at the relay and the destination. Our analysis assumes Rayleigh fading for the source-relay and relay-destination channels and Rician fading for the interfering channels. We present new closed-form/series expressions for the outage probability and the average BER. The achievable diversity order is also studied. It is further shown through numerical results that the Rician K-factor of the interfering channel has a negative effect on the overall outage probability and BER, yet this effect is very small.