BiNi clusters have been studied using the hybrid B3LYP density functional and diffusion quantum Monte Carlo (DMC) methods. Different cluster families have been characterized for each cluster size using B3LYP, and the energy differences have been compared with those obtained within DMC. The DMC results predict that the global minimum energy structures are rings for i = 2-9, a three-ring structure for i = 10 and spheroids for i greater than or equal to 11. The aromaticity of the ring structures has been studied using the nuclear independent chemical shifts (NICS) criterion. According to this criterion, rings with an odd number of BN units are aromatic. Aromatic structures are thought to be the most stable, and the DMC results for the most stable structures are consistent with this hypothesis, but in some cases, the B3LYP results are not.