Hyperostosis cranialis interna is a hereditary bone disorder that is characterized by endosteal hyperostosis and osteosclerosis of the calvaria and the skull base (OMIM 144755). The progressive bone overgrowth causes entrapment and dysfunction of cranial nerves I, II, V, VII, and VIII, its first symptoms often presenting during the second decade. This study analyzes the clinical course of 13 affected individuals of three related families (32 individuals). The disorder appears to have an autosomal-dominant transmission pattern. Facial and vestibulocochlear nerve dysfunction are most frequently reported. Surgical decompression of the accessible impaired cranial nerves is advised in the early symptomatic period or even in the presymptomatic period in high-risk individuals.