The cardid bivalve Acanthocardia tuberculata is harvested in southern Spain and on the Atlantic coast of Morocco for the Spanish canning industry. The reproductive cycle and population structure of this species were studied in southern Spain from June 1999 to May 2000, using histology and condition indices, as well as modal size classes in length-frequency distribution analysis. The samples were collected monthly during autumn and winter months and fortnightly during spring and summer months. A total of 4,047 specimens were examined, from which 3,539 specimens were processed for biomass analyses and 508 for the study of the gametogenic cycle. Shell lengths of individuals ranged from 6 to 76 mm (48.15 ± 15.15 mm, mean ± SD), and the sex ratio was 1:1. The reproductive cycle of A. tuberculata showed an annual pattern, with an extended sexual activity from January to July, during which successive spawning events were observed, and with a clear-cut resting period from September to November. Small-size individuals are recruited into the population from June to December. No correlations were found between the environmental variables (sea water temperature and concentration of chlorophyll a) and the condition indices, which could be explained by the presence of upwellings in the area that introduce random fluctuations of these environmental variables. To improve management of the wild stock, a closed season during June–July was proposed together with a minimum harvest size of 45 mm.