Fault diagnosis is important for the immediate elimination of faults in a network. Over the years the diagnosis of faults for a single path network is frequently reported but that for a multipath network remains relatively unattended. The goal of this research is to detect faults in the gamma interconnection network (GIN) and the cyclic gamma interconnection network (CGIN), two multistage interconnection networks (MINs) with multiple paths. Two approaches, the primary fault diagnosis approach and the advanced fault diagnosis approach, are proposed. The primary approach can be employed to detect and locate either a single fault or multiple faults in GINs and CGINs; the advanced approach is able to detect a single fault with much reduced detection time. For better illustration, examples are given following the presentation of each approach for both multipath networks. Extended simulation is conducted to demonstrate the effectiveness of the proposed approaches.