An account of the breeding colony of grey seals on North Rona, between 3rd and 25th October, 1959, is given. Six censuses of the pups and moulters were made between those dates and more detailed censuses of one part of the colony (Fianuis Central) are recorded. The breeding season extends at least from the beginning of September until mid-November and the total number of pups born exceeds 2,300. Mortality on land up to 16th October averages 17 per cent. In addition, those born on the rock “foreshore” are almost all certainly lost. A description of the behaviour of the cows, bulls and moulters is given. The ratio of bulls to cows is estimated to lie between 1: 10 and 1: 13.