The outage probability performance of a dual-hop amplify-and-forward (AF) selective relaying system with global relay selection is analyzed for Nakagami- m fading channels in the presence of multiple interferers at both the relays and the destination. Two different cases are considered. In the first case, the interferers are assumed to have random number and locations. Outage probability using the generalized Gamma approximation (GGA) in the form of 1-D integral is derived. In the second case, the interferers are assumed to have fixed number and locations. Exact outage probability in the form of 1-D integral is derived. For both cases, closed-form expressions of lower bounds and asymptotic expressions for high signal-to-interference-plus-noise ratio (SINR) are also provided. Simplified closed-form expressions of outage probability for special cases (e.g., dominant interferences, independent identically distributed (i.i.d.) interferers, and Rayleigh distributed signals) are studied. Numerical results are presented to show the accuracy of our analysis by examining the effects of the number and locations of interferers on the outage performances of both AF systems with random or fixed interferers.