Lentigines, synonymous but not identical to freckles or ephelides, are common skin lesions. In a small number of patients, however, these lesions constitute part of genetic syndromes that are associated with inherited forms of neoplasias or other pathologic processes of the cardiovascular, endocrine, and gastrointestinal systems. The familial lentiginoses, as these syndromes are collectively known, include Carney complex, the LEOPARD and Peutz-Jeghers syndromes, and the newly described 'syndrome of arterial dissections with lentiginosis'; isolated, familial lentiginosis has also been described. In the majority of the reported kindreds with these syndromes, the lesions were inherited in an autosomal dominant manner. The specific genes that are responsible for these disorders have remained elusive, but the genetic loci of Carney complex and Peutz-Jeghers syndromes were recently identified on chromosomes 2p 16 and distal 19p, respectively. Cytogenetic studies of tumours from patients with Carney complex suggest that the gene responsible for most patients with this syndrome may not have a tumour suppression function. We suggest that the genes responsible for the lentiginosis syndromes are important regulators of melanocyte function, they participate in the pleiotropy of human pigmentation, and are involved in the function, growth and proliferation of neural crest and mesenchymal cells.