Skin fibroblast cultures from a female patient with dyskeratosis congenita revealed markedly increased frequencies of chromosomal breaks, hypodiploidy, and premature centromere disjunction. The frequencies of mitotic disturbances, like ana- and telophase bridges, lagging chromosomes, and micronuclei were almost as dramatically elevated as in cultures from two severely affected patients with Fanconi anemia. Provided that our patient is representative for an autosomal form of dyskeratosis congenita, this type of the disease seems to be characterized by chromosomal instability with a characteristic pattern of cytogenetic abnormalities.