The fecundity of Liocarcinus depurator (Decapoda: Brachyura) in the Ría de Arousa (Galicia, north-west Spain) and the reasons why it fluctuates were analysed, comparing the results with data available from other geographical areas. The incubation of L. depurator eggs in the Ría de Arousa generally takes place between January and September, although ovigerous females can be found all year round. The number of eggs per brood in L. depurator varied considerably in the Ría de Arousa and ranged from 5265 (carapace width (CW=31·3 mm, stage III) to 203,724 (CW=44·6 mm, stage I). The allometric equations adjusted to fit each egg development stage indicated that there was a strong positive correlation between female body size and the number of eggs the animal is able to bear. Female body size, measured as the carapace width, was the main factor causing variability in the fecundity of L. depurator. The second most important cause of variability in the development stages of the eggs was the number of eggs per brood, which may be due to the gradual loss of eggs that occurred during the incubation of these eggs in the female abdomen. Temporal changes constituted another significant factor in the variability of the fecundity of L. depurator. The allometric equations (log F=log a+b×log CW) fitted to each month and development stage I presented changes in the slope which point to the existence of a temporal evolution in the number of eggs. In the Ría de Arousa and for all the development stages, L. depurator was found to have a significant negative correlation between the number of eggs per clutch and egg volume. Egg volume also correlated negatively with the size of the female in stages I of the egg development. The degree of correlation between the volume and number of eggs was greater than the correlation between volume and size. The main cause of the variability in the egg volume of L. depurator in the Ría de Arousa may be attributed to the development stage (ANCOVA, P<0·001).