Hyperostosis generalisata with striations of the bones falls within the large group of sclerotic bone dysplasias and is characterised by a marked widening of cortical bone, sclerosis of the base of the skull, and dense striations in the cancellous bone. All the bones of the skeleton, with the possible exception of the vault of the skull, may be involved to some extent. A milder form exists in which thickening of cotrical bone occurs, mainly in the long bones of the limbs and striations are absent. The disorder has never been described in the female. Apart from a slight elevation of the serum alkaline phosphatase in some patients, no significant biochemical changes and no impairment of intelligence, growth, or life expectancy have been found. The diagnosis is made entirely on its radiological features. Its occurrence in four members, covering two generations, and three members, covering three generations, of two related families is described. A possible relationship to progressive diaphyseal dysplasia (Camurati--Englemann disease) is discussed.