Several life-history features of Niagara River muskellunge were determined and compared to similar data for other populations. Sexual maturity occurred during the fourth and fifth year for most Niagara River males and females, respectively. In terms of ages at sexual maturity and length-weight relationship, Niagara River muskellunge were similar to lake populations. In early life, fish of the Niagara River, and those of West Virginia and Kentucky streams, grew more rapidly than fish from lake populations. However, growth of river and stream fish slowed more quickly with age than that of lake fish. These differences in growth pattern between lentic and lotic populations may have resulted from differences in prey sizes and availability.