One hundred and three patients with cutaneous malignant melanoma responded to an invitation to attend a dermatology outpatient clinic. All patients with a family history of melanoma, a history of multiple melanomas, or histological evidence of a dysplastic naevus that was associated with their melanoma were invited. A random sample of other patients with cutaneous malignant melanoma was also invited to attend. First-degree relatives of patients with the dysplastic naevus syndrome (DNS) were invited for a similar examination. DNS was found in 27% of the patients with a family history of melanoma, multiple melanomas, or histological evidence of a dysplastic naevus in association with their melanoma, and in 6% of the remaining patients who were selected at random. DNS was estimated to be present in 12.8% of 17- to 55-year-old patients with cutaneous malignant melanoma in the Perth region, while familial DNS was present in 4.5%. Patients with melanomas with DNS were more likely to be young men and to have numerous naevi, particularly on the lateral surfaces of the arms, shoulders and trunk, than were patients with melanomas without the syndrome.