Under current Spanish regulations, the pigs that provide the raw material for the preparation of the country's most appreciated meat-derived product, dry-cured Iberian ham, must be of a specific genetic composition. Only the Duroc breed is accepted for crossing with Iberian pigs, and a maximum of 50% of the Duroc genome is permitted in the animals used to make this ham. This paper describes a set of statistical procedures for detecting the 'breed composition' of Iberian ham via the use of multilocus genotypes obtained by the amplification of 25 microsatellite markers. The proposed procedure detected up to 20% of ham samples with a genetic composition incompatible with present legislation - either because the Duroc genome was present in a percentage greater than that permitted, or because of the significant presence (>25%) of white coat pig genomes. The probability of finding an illegal cured ham was greater in restaurants than in retail grocery stores, and in medium-low category restaurants or stores than in higher category establishments.