Carrier probabilities were calculated in 27 Duchenne muscular dystrophy (DMD) families with 68 possible carriers on whom carrier testing data were available. For each of the 68 possible carriers, eight different calculations were performed. The calculations differed by leaving out none, one, two or all three of the following different types of posterior information: the result of carrier testing in the consultand; the presence of unaffected sons of possible carriers in the family; the result of carrier testing in possible carriers, other than the consultand. All three types of posterior information proved to be equally important. Our data thus provide evidence in favour of the whole family approach in DMD genetic counselling as opposed to counselling of isolated DMD relatives.