Hook size is an important consideration in the use of circle hooks as a conservation tool for minimizing the injury and mortality of marine fishes, but little is known about the role of hook size in the performance of hooks in recreational freshwater fisheries. In this study, we angled 100 bluegills Lepomis macrochirus on each of five different‐sized circle hooks (1/0, 2, 6, 10, and 14). The largest hook size (1/0) had low hooking and capture efficiency but selected larger individuals. The smallest hook size also had low hooking efficiency and resulted in the selection of smaller individuals. Intermediate hook sizes captured fish of intermediate size. Jaw hooking rates generally increased with decreasing hook size, whereas roof hooking rates decreased. Gullet hooking was restricted to the three smallest hook sizes. Relative hooking depth and incidences of bleeding were uniformly low for all hook sizes. Similarly, the fish were generally easy to remove from the hook irrespective of hook size. Our mortality projections revealed no trends associated with hook size, our overall mortality rate being less than 1%. This study suggests that circle hooks function most effectively when the entire hook can fit in the mouth of the fish and when the shank‐to‐point distance is large enough to permit jaw hooking. Size selectivity for larger individuals can be achieved by using larger hook sizes. However, large circle hooks will also catch smaller fish that will be more likely to be hooked in injurious anatomical locations. Therefore, we recommend the use of intermediate‐sized hooks for maximizing hook performance in terms of size selectivity, efficiency, and conservation.