A yearlong study was carried out to investigate the presence and viability of Cryptosporidium oocysts in 203 samples of cultured shellfish from Galicia (NW Spain) and 38 samples imported from other European Union (EU) countries. Shellfish samples included mussels, oysters, clams and cockles. Cryptosporidiumoocysts were detected, using a direct immunofluorescence antibody test (IFAT), in 34.4% of the samples analyzed; use of the fluorogenic dye propidium iodide (PI) revealed viable potentially infective oocysts in 53. 0% of these samples. There was no relation between the presence of Cryptosporidium oocysts and the microbiological contamination detected in the samples expressed as Most-Probable-Number (MPN) of fecal coliforms, the different species of mollusc, or the month of sampling. One important finding was that the depuration process was ineffective in totally removing oocyst contamination. Furthermore, the existence of viable oocysts in samples with microbiological contamination levels lower than 300 fecal coliforms/100 g, which in accordance with current legislation are considered suitable for human consumption, suggests the need to include parasitological analyses in the quality control for these molluscs.