A commercial fishery for gcoduck Panopea generosa in Baja California began in 2002 and has since achieved landings comparable with those in Washington state and British Columbia, Canada, where geoduck fisheries developed in 1970 and 1976, respectively. This investigation was motivated to acquire the knowledge of population biology of P. generosa at the southernmost extent of its distribution that is required to establish a biological basis for fishery management decisions. This article was further motivated to assess the appropriateness of the current minimum legal size of 130 mm established by the Mexican fishing authorities. Morphometric relationships, age, and growth, and natural mortality of P. generosa were investigated with animals collected from Bahía de San Quintin and Islas Coronado, Baja California, Mexico, collected monthly from April 2008 through January 2009. Ages were obtained by counting growth bands in cross-sections of the shell hinge plate and utilizing cross-dating methods to increase accuracy. Individual P. generosa ages ranged from 3–96 y over both sites. Growth is rapid during the first 10 y and then slows for individuals older than 20–25 y. The asymptotic length was found to be 134 mm, the mean total weight was 764 ± 255 g, the Brody growth coefficient (k) was 0.191, and the natural mortality rate was estimated to range from 0.027–0.046, depending on the method used. These parameter values are similar to those of more northern populations of the same species. Because the proposed minimum legal size is close to the asymptotic length, and considering that geoduck size is difficult to determine before harvest, we suggest that the use of a minimum legal size is not an effective management strategy for geoduck clams.