A study based on fifteen pedigrees showed that familial glomus tumours are inherited almost exclusively via the paternal line, a finding inconsistent with autosomal dominant transmission. The results can be explained in terms of the genomic imprinting hypothesis--the maternally derived gene is inactivated during female oogenesis and can be reactivated only during spermatogenesis. Genomic imprinting may have considerable implications for genetic counselling with respect to glomus tumours and also for the understanding of other hereditary diseases.