Information from 6273 registered in the flockbook of the Mallorquina sheep breed was analysed. Up to 34.3% of the individuals had registered parents and 7.6% registered grand-fathers. Average generation interval was 3.7 years. The effective number of founder herds (11.1) was roughly a quarter of the real one. The effective number of herds supplying rams was 8.8 for fathers and 3.8 for grandfathers. The equivalent number of founders was 4122 which was 66% of the total analysed animals. The effective number of founders was 704 (17% of the equivalent number of founders). The effective number of ancestors for the Mallorquina population was 90, and 50 ancestors would explain 50% of the total genetic variability of the population. Average values for inbreeding, average relatedness and equivalent to discrete generations were 0.24%, 0.17% and 0.43, respectively. Only 121 inbred individuals were found with average values for the former parameters of 17.93%, 0.92% and 1.91. A few within-flock bottlenecks have been detected and, as a consequence, inbred individuals appeared. However, no risk for the genetic variability of the breed arose.