The prevalence, pattern of inheritance, and phenotype of Darier's disease was examined in a cross-sectional study of cases in north-east England. Seventy-five cases, representing a local prevalence of at least 1:36,000, were identified and examined. Forty-two cases were known to dermatologists, and 33 were identified in the course of the study: 60 were adults (above the age of 20) and 15 were children. In nine families, 66 of 136 adults with an affected parent were known to be affected, indicating complete penetrance of an autosomal dominant gene. eighteen individuals gave no family history, but seven of these were found to be members of affected kindreds and five obligate carriers examined all proved to have evidence of the disease. In other 'new' cases, including several whose parents were examined and confirmed to be normal, no relationship to other cases was found. These cases probably represent new mutations or non-paternity rather than incomplete penetrance. All but one adult case had the typical rash, but it was milder in women; 16/18 adults who had not presented to dermatologists were female. Diagnostic nail lesions were found in 59 (99%), palmar pits and keratoses in 57 (95%), and acrokeratosis verruciformis in 44 (73%). In 15 young cases (aged 5-18) with one or more diagnostic features, the rash was found in only four (27%), nail lesions in nine (60%), palmar pits in eight (53%), and acrokeratoses in ten (67%). The minor lesions were often subtle but were more consistent early evidence of disease than the rash, and even in the absence of a rash gene penetrance may be complete by the age of 10.