The seasonal brood size of the spiny lobster Panulirus gracilis in Mexican waters (southeastern Gulf of California) was estimated for 259 ovigerous females caught in commercial tangle nets at depths ranging from 8–25 m during spring, summer, fall, and winter between March 1993 and March 1994. The number of eggs per individual ranged from 76,727 eggs for a 60.0-mm carapace length (CL; 250 g total weight (TW)) female to 1,115,060 for a 80-mm CL (510 g TW) female. A brood size (BS) value was estimated from replicate counts and was found to vary with CL and TW according to the relationships BS = 0.6803CL^3.1007 (R²= 0.5203) and BS = 1236.7TW - 35548.9 (R² = 0.5781), respectively. The smallest egg-bearing female was 50.3 mm in CL. Significant differences were found in seasonal brood sizes, with lower values during the winter than during the remaining seasons. Egg loss during the incubation period was estimated at 7.9%.